Power
and Size:
Urbanization and Empire
Formation in World-Systems Since the Bronze Age
Christopher Chase-Dunn
Alexis Álvarez
Daniel Pasciuti
V 4-13-04 (8041 words) Revised version.
World-systems are
intersocietal interaction networks in which culturally different peoples are
strongly linked together by trade, political-military engagement and
information flows. This chapter presents an overview of research on city and
empire growth/decline phases and new evidence on the relationship between urban
growth and the rise and fall of empires in six regions that once contained
substantially separate world-systems.[1]
We find that empires and cities grow and decline together in some regions, but
not others, and we examine the temporal correlations between growth/decline
phases of largest and second largest cities and empires within regions. Do
large empires grow at the expense of other large states within a region or are
there periods of regional growth in which states (and cities) are growing
together?
Earlier research has demonstrated the utility of
studying settlement systems and networks of interacting polities as windows on
the historical development of social complexity and hierarchy (Chase-Dunn and
Hall 1997). By knowing the population sizes of settlements and the approximate
territorial sizes of states and empires we can compare rather different time
periods and regions in order to discover both regularities and uniquenesses.
This chapter summarizes the results
of earlier studies using city and empire sizes and presents new results on the
relationships between changes in urban populations, city-size distributions and
the territorial sizes of states and empires. Archaeologists often assume that
the concentration of political power can be inferred from the rise of a size
hierarchy of settlements – increases in the steepness of the settlement size
distribution (e.g. Kowalewski 1982). Existing data can be used to test this
hypothesis, though more certain results await the improved accuracy and greater
temporal resolution of estimates of city and empire sizes.[2]
Chase-Dunn and Willard (1993)
examined urban growth and city-size distributions[3]
in nine different regional political/military networks (PMNs) [4]
using data on city sizes from Tertius Chandler’s (1987) compendium.
Political/military networks (PMNs) are interstate systems – systems of adjacent
conflicting and allying states. David Wilkinson (1987) bounds these expanding
and contracting systems of states as they merge or become incorporated into
what Wilkinson calls the “Central Civilization.” Chase-Dunn and Willard (1993)
plotted changes in the Standardized Primacy Indices (a measure of the steepness
of the city-size distribution) over time, and read descriptions of what was
happening in nine different PMNs to examine the hypothesis that changes in the
city-size distribution are related to changes in the centralization of state
power in regional state systems. They
also accidentally discovered a synchrony of changes in city size distributions
and phases of urban growth/decline in the East Asian and the West
Asian-Mediterranean PMNs over a long period from 650 BCE to 1500 CE.[5]
This latter discovery led to further research
using data on the territorial sizes of empires gathered by Rein Taagepera
(1978a, 1978b, 1979,1997). That analysis (Chase-Dunn, Manning and Hall 2000)
found additional evidence for synchrony between the East Asian and the West
Asian-Mediterranean PMNs over this same 2150-year period, and confirmed what
had also been indicated by scant city size data from India, that the Indic PMN
was marching to a different drummer.
These synchrony results were further confirmed by additional analysis of the city data by Chase-Dunn and Manning (1998). That study examined inter-regional synchrony by comparing constant regions rather than PMNs. PMN boundaries change over time because of the expansion of the Central PMN, whereas specified regions that are held constant over time constitute a different, but related, unit of analysis. Chase-Dunn and Manning found support for the East/West synchrony phenomenon using constant regions, and so this result is not likely to be an artifact of the way in which units of analysis have been constructed.
Power,
Urban Growth and Urban Size Hierarchies
This chapter returns to the question
asked in the Chase-Dunn and Willard (1993) study about the relationship between
urban growth, city-size distributions and the rise and fall of empires. What is
the relationship between the size of settlements and power in intergroup
relations? Under what circumstances does a society with greater population
density have power over adjacent societies with lower population density, and
when might this relationship not hold?
Population density is often assumed to be a sensible proxy for relative
societal power. Indeed, Chase-Dunn and Hall employ high relative population
density as a major indicator of core status within a world-system (Chase-Dunn
and Hall 1997). But Chase-Dunn and Hall are careful to distinguish between
“core/periphery differentiation” and “core/periphery hierarchy.” Only the
latter constitutes actively employed intersocietal domination or exploitation,
and Chase-Dunn and Hall warn against inferring power directly from differences
in population density.
In many world-systems military
superiority is the key dimension of intersocietal relations. Military
superiority is generally a function of population density and the proximity of
a large and coordinated group of combatants to contested regions. The winner of
a confrontation is that group that can bring the larger number of combatants
together quickly. This general
demographic basis of military power is modified to some extent by military
technology, including transportation technologies. Factors such as better
weapons, better training in the arts of war, faster horses, better boats,
greater solidarity among soldiers and their leaders, as well as advantageous
terrain, can alter the simple correlation between population size and power.
Ironically, George Modelski’s (2003) important study of the growth of world
cities completely ignores the phenomenon of state and empires sizes, though
Modelski is himself an astute scholar of international relations and
geopolitical power. Modelski contends that cities are the most important
driving force of world system evolution and that we may conveniently ignore
states and empires. We think that the relationship between political power and
settlement systems may have changed over the millennia, so that the explicit
analysis of the relationships between size and power needs to be directly
examined.
The most important general exception
(in comparative evolutionary perspective) to the size/power relationship is the
phenomenon of semiperipheral development (Chase-Dunn and Hall
1997:Chapter 4). The pattern of uneven
development by which formerly more complex societies lose their place to “less
developed” societies takes several forms depending on the institutional terrain
on which intersocietal competition is occurring. Less relatively dense semiperipheral marcher chiefdoms conquer
older core chiefdoms to create larger chiefly polities (Kirch 1984). Likewise,
semiperipheral marcher states, usually recently settled peripheral peoples on
the edge of an old region of core states, frequently are the agents of a new
core-wide empire based on conquest (Mann 1986; Turchin 2003).[6]
Another exception is the phenomenon of semiperipheral capitalist city-states –
states in the interstices between tributary empires that specialized in
long-distance trade and commodity production.
Though these were rarely the largest cities within the world-systems
dominated by tributary empires, they played a transformational role in the
expansion of production for exchange and commodification in the ancient and
classical systems. And less dense semiperipheral Europe was the locus of a
virile form of capitalism that condensed in a region that was home to a large
number of unusually proximate semiperipheral capitalist city-states. This
development, and the military technology that emerged in the competitive and
capitalist European interstate system, made it possible for less dense Europe
to erect a global hegemony over the more densely populated older core regions
of Afroeurasia (Chase-Dunn and Hall 1997). The more recent hegemonic ascent of
formerly semiperipheral national states such as England and the United States
are further examples of the phenomenon of semiperipheral development.
The phenomenon of semiperipheral
development does not totally undermine the proposition that societal power and
demographic size are likely to be correlated. What it implies is that this
correlation can be overcome by other factors, and that these processes are not
entirely random. Denser core societies are regularly overcome or out-competed
by less dense semiperipheral societies, but it does not follow that all
semiperipheral or peripheral regions have such an advantage. On the contrary,
in most world-systems most low-density societies are subjected to the power of
more dense societies. Semiperipheral
development is a rather important exception to this general rule.
Why should a city system have a steeper size
distribution when there is a greater concentration of power? The simple answer
is that large settlements, and especially large cities, require greater
concentrations of resources to support their large populations. This is why
population size has itself been suggested as an indicator of power (Taagepera,
1978a: 111). But these resources may be obtainable locally and the settlement
size hierarchy may simply correspond to the distribution of ecologically
determined resources. People cluster near oases in a desert environment. In
such a case it is not the political or economic power of the central settlement
over surrounding areas that produces a centralized settlement system, but
rather the geographical distribution of necessary or desirable resources. In
many systems, however, we have reason to believe that relations of power,
domination and exploitation do affect the distribution of human populations in
space. Many large cities are as large as they are because they are able to draw
upon far-flung regions for food and raw materials. If a city is able to use
political/military power or economic power to acquire resources from
surrounding cities it will be able to support a larger population than the
dominated cities can, and this will produce a hierarchical city size
distribution.
Of course the effect can also go the other way.
Some cities can dominate others because they have larger populations, as
discussed above. Great population size makes possible the assembly of large
armies or navies, and this may be an important factor creating or reinforcing steep
city size distributions.
The relationship between power and settlement
systems is contingent on technology as well as political and economic
institutions. Thus we expect to find that the relationship between urban growth
and decline sequences and the growth/decline sequences of empires varies across
different systems or in the same regional system over time as new institutional
developments emerge. We know that the development of new techniques of power,
as well the integration of larger and larger regions into systems of
interacting production and trade, facilitate the emergence of larger and larger
polities as well as larger and larger cities. Thus, there is a secular trend
at the global level and within regions between city sizes and polity sizes over
the past six millennia. But the question we are asking here is about finer
temporal and spatial relationships. Do cities and empires rise and fall
together? Are there important exceptions to this pattern? What are the
causalities involved?
We may also ask whether or not the causal
relations are stable over time within regions? We expect that there may be
periodic changes in the relationship between power and size as new institutions
develop. The rise of capitalism as an alternative source of power to military
might and changes in the relationship between military power and demographic
factors most likely change the nature of the connections between size and
power. We know that empires ceased to increase in territorial size with the
demise of the modern colonial empires. And the contemporary world city system
may be unique in the extent to which some of the largest cities are located in
the semiperiphery rather than in the core. The exponential growth of cities
after 1800 CE makes it more difficult to study growth/decline phases because
the largest cities no longer decline in size.
We will further examine the
relationship between power, urban growth and settlement size hierarchies by
comparing trends in the growth/decline sequences of city populations and the
territorial sizes of empires. The main unit of analysis in this study will be Constant
Regions[7]
rather than political/military networks (interstate systems). We shall also consider studying individual
polities (states and empires), because the simplest form of the hypothesis of a
causal relationship between power and urbanization is that larger states can
afford to create larger cities. But available data are not sufficient for
studying the power/size relationship within individual polities except for relatively
recent states.
And
we will examine the temporal relations between the sizes of the largest cities
and empires in each region as well as size distributions of cities and empires
and the relations between the largest and the second largest cities and empires
when data are available.
Measurement of the population sizes
of cities and the territorial sizes of empires is not without difficulties,
especially for early periods. How can we know the number of people who reside
in Los Angeles today? We use the most recent census, a survey of “residents”
conducted by the U.S. federal government. What are the spatial boundaries of
“Los Angeles”? Do we mean the city of Los Angeles, Los Angeles County, the
contiguous built-up area that constitutes “greater Los Angeles,” or a
definition based on the proportion of the local population that is employed in
“Los Angeles”? Does “Los Angeles” include San Diego? Nighttime satellite photos
of city lights reveal a single unbroken megalopolis from Santa Barbara to
Tijuana (see Figure 1).
Figure
1: Southern California / Northwestern Mexico conurbation (city lights from
satellite photographs).
So where is Los Angeles? We want to use the contiguous
built-up area as our main way of spatially defining cities, another example
being the New England urban agglomeration (see Figure 2). For early cities we do not have official,
and ostensibly complete, census figures. Thus we rely on methods that
archaeologists and students of early urbanization have developed to estimate
the population sizes of cities.
Figure
2: New England conurbation (city lights from satellite photographs).
These involve, for example, determining the
spatial size of the city and then estimating the population density per unit of
area and so estimating the total population (city size * density = city
population). Population density varies depending upon the size of families, the
nature of dwellings, the amount of non-residential area within settlements, and
cultural differences. Anthropologists and archaeologists have made an important
effort to produce reliable methods for estimating population sizes from
residential areas (e.g. Brown 1987), and the famous historical demographer Paul
Bairoch (1988: 21-4) has examined the problem of urban population densities in
comparative perspective.
Tertius Chandler (1987) used reports about the number of soldiers to estimate city sizes, assuming that an army represents, on the average, about ten percent of the population of the city in which the army resides. Such estimates are obviously error-prone. Another problem with existing data on both city and empire sizes is that they were produced from surveys of both secondary and primary sources that are now, in many cases, obsolete because more recent and better research has been published by archaeologists, epigraphers and historians. Chandler’s compendium was mainly based on his thorough survey of the contents of the main library at the University of California, Berkeley over the four decades prior to its publication in 1987. We also use the new estimates of city population sizes produced by George Modelski’s (2003) important study. A new project to improve upon existing compendia of city sizes is under way at the Institute for Research on World-Systems at the University of California, Riverside (Pasciuti 2003).
Estimating the territorial sizes of
empires is also problematic. Taagepera used atlases and maps to produce his
estimates of the spatial sizes of empires from 3000 BCE to the present. But the
boundaries of empires are not usually formally specified, but are rather a
matter of degrees of control that fall off with distance from the central
region. Archaeological evidence of the presence of a core culture in a
peripheral region does not prove the existence of control, because many core
polities have established colonial enclaves in distant peripheries to
facilitate trade (e.g. Stein 1999). So the estimation of empire sizes is also
fraught with difficulties. But, as with city sizes, a significant improvement
of accuracy, temporal resolution and coverage would result from a renewed
effort to code empire sizes using recently published materials. This is another
task that the IROWS City-Empire Research Working Group will undertake.[8]
Dating is also a major problem in
studying temporal relationships in the ancient world-systems. In this paper we
utilize the years originally supplied by Taagepera and Chandler. But the dating
of events and city size estimations for the first millennia BCE is a matter of
continuing dispute among scholars of ancient history. For ancient Western Asia
the Egyptian dynastic dates are used, but these have been repeatedly revised
with an error margin of around 25 years. This is a threat to any study of
temporal correlations.
Mesopotamia
The first PMN we shall examine is that of Mesopotamia from 2800 to 550 BCE. It is mistaken to speak of a single West Asian/North African world-system for this whole period. Rather two core areas – Egypt and Mesopotamia – were undergoing developmental processes that were only weakly linked, especially at first. As both of these systems expanded their trade networks and political/military interaction networks they came into contact with one another. The prestige goods nets (PGNs) became linked as early as 3000 BCE (Marfoe 1987) or as late as 2250 BCE (Wilkinson 1992), while the Mesopotamian and Egyptian political/military networks became linked by the Egyptian expedition to Syria (about 1520 BCE). We examine the relationships between the population size of the largest city and the territorial size of the largest state or empire in a region as these change over time. The hypothesis of a correspondence between urbanization and the size of polities should reveal a positive correlation in these two measures over time. The data on city population sizes are especially sparse for early millennia and the time points of estimates are widely spaced, making temporal correlation risky. For Mesopotamia our data set is thus:
|
Year (BCE) |
Empire Size (MM2) |
Empire Name |
City Name |
City Pop
(thousands) |
|
-2800 |
1 |
Kish |
Uruk* |
80 |
|
-2500 |
3 |
Kish |
Uruk* |
50 |
|
-2400 |
5 |
Lagash |
|
|
|
-2300 |
65 |
Akkadian |
Agade*# |
36 |
|
-2200 |
25 |
Akkadian |
|
|
|
-2100 |
3 |
Ur |
|
|
|
-2000 |
10 |
Sumer |
Ur |
65 |
|
-1900 |
0 |
|
|
|
|
-1800 |
10 |
Old Assyria |
Mari |
29 |
|
-1700 |
25 |
Babylon |
|
|
|
-1600 |
16.6 |
Babylon |
Babylon |
60 |
|
-1500 |
10 |
Kassite |
|
|
|
-1450 |
10 |
Kassite |
|
|
|
-1400 |
10 |
Kassite |
|
|
|
-1360 |
21.7 |
Hittites |
Khattushash
(Hattusa) |
45 |
|
-1350 |
5 |
Assyria |
Khattushash
(Hattusa) |
45 |
|
-1300 |
10 |
Assyria |
|
|
|
-1250 |
15 |
Assyria |
|
|
|
-1200 |
25 |
Hittites |
Khattushash (Hattusa) |
48 |
|
-1150 |
5 |
Assyria |
|
|
|
-1100 |
40 |
Assyria |
|
|
|
-1050 |
15 |
Babylon |
|
|
|
-1000 |
15 |
Babylon |
Babylon |
51 |
|
-950 |
15 |
Babylon |
|
|
|
-900 |
15 |
Babylon |
|
|
|
-850 |
40 |
Assyria |
|
|
|
-800 |
57.9 |
Assyria |
Calah |
50 |
|
-750 |
40 |
Assyria |
|
|
|
-700 |
90 |
Assyria |
|
|
|
-650 |
93.3 |
Assyria |
Nineveh |
120 |
|
-600 |
25 |
Babylon |
|
|
|
-550 |
50 |
Babylon |
|
|
Table 1:Mesopotamian Largest Empires and Cities
*These estimates are
from Modelski (2003). All other estimates are based on Chandler and Taagepera.
#Archaeologists have
not yet decided which of the thousands of tells in Iraq is Agade, the capital
of Sargon’s Akkadian empire.
Table
1 immediately demonstrates problems of missing data, especially for the third
millennium. The time points for city sizes are far apart, and there are
obviously missing cases. We have Modelski’s (1997) best estimate of the
population size of Uruk in 2800 and 2500 BCE, but the largest empire shown in
Taagepera’s data is that of Kish, a city-state that was independent of the much
larger empire of Uruk in this period. This obvious error strongly demonstrates
the need for upgrading the data sets we are using. In the data presented in
Table 1 and in the figures and tables below we have interpolated Taagepera’s
dates of changes in the sizes of empires to regular time intervals (every 50
years in Table 1 and Figures 3 and 4; every 10 years for the other regions in
Table 2 and the figures in Appendix A, (see http://www.irows.ucr.edu/research/citemp/appendices/apppowsize.htm).
Another complication revealed in
Table 1 is as follows: in 1350 and 1200 BCE the largest city is Khattushash (Hattusa),
the capital of the Hittite empire, but the largest empire in the Mesopotamian
region is the Neo-Assyrian Empire. This raises the issue of the proper unit of
analysis – regions or polities – but it also raises a theoretical issue. The
simplest version of the size-power hypothesis is that larger empires can afford
larger cities, and to test this hypothesis we would need temporally
fine-grained data on the size of the largest city within each empire.
For this purpose the unit of analysis should be the polity (states and
empires). But it may also be the case that regions or PMNs experience cyclical
periods of growth and decline in which all the states and cities are growing,
or alternatively that state and city growth is a zero-sum game in which growth
in some results or is related to decline in others. By using and comparing
different spatial units of analysis we can examine these competing hypotheses.
Figure 3: Largest Mesopotamian Cities and Empires
The temporal relationship between the size of the
largest city and the size of the largest empire is positive for the
Mesopotamian case with a positive Pearson’s r correlation coefficient of .45
based on twelve time points for which we have data for both variables (see
Figure 3). This supports the hypothesis of a causal relationship between these
features of the social landscape, but the positive association could also be
due to other factors or to the secular trending of these characteristics. We
will return to these issues when we have more and better data in the cases to
be discussed below.
Egypt
As
with Mesopotamia the data for Egypt are few and problematic. But using what we
have produces the results displayed in Figure 4.
Figure 4: Largest Egyptian Cities and Empires
The temporal relationship between city and empire
sizes in Egypt is also positive, producing a Pearson’s r correlation
coefficient of .06 based on eight time points for which we have data for both
variables. Though there is a secular upward trend, both city and empire sizes
also reveal decline phases and these are roughly synchronous with one another,
though the few estimates of city sizes makes a firm conclusion risky.
Size and Power in Regions
Table 2 (below) presents the
bivariate Pearson’s r correlation coefficients between empire and city sizes
for all of the regions for which we have sufficient data. It also presents the
partial correlations controlling for year to remove the long-term upward trend
between city and empire sizes. The Americas and Africa do not have enough city
size data, though this deficiency could and should be remedied by a new coding
project.
Table 2 shows that five of the six
regions have statistically significant positive bivariate correlations between
city and empire sizes. This lends support to the contentions discussed above of
a causal interaction between power and size, but these correlations do not shed
light on the question of the direction of the causal effects. Once we have
improved data we plan to employ the test of antecedence to shed light on this.
We should also note the two of our regional “cases” overlap with one another,
Mesopotamia and West Asia.
|
|
Correlations
between 3-period moving averages of city and empire sizes |
||||
|
|
|
|
|
|
|
|
|
Region |
Bivariate r |
Partial r |
Biv. N |
Years |
|
|
Egypt |
0.373 |
0.152 |
8 |
2800 B.C.E. - 1500
B.C.E. |
|
|
Mesopotamia |
0.699** |
0.492* |
18 |
2800 B.C.E. - 650
B.C.E. |
|
|
West Asia |
0.542** |
0.207^ |
44 |
2800 B.C.E. - 1500
C.E. |
|
|
South Asia |
0.593* |
0.578* |
13 |
1800 B.C.E. - 1500
C.E. |
|
|
East Asia |
0.610** |
-0.191 |
33 |
1360 B.C.E. - 1800
C.E. |
|
|
Europe |
0.510** |
0.7324** |
29 |
430 B.C.E. - 1800
C.E. |
|
|
|
|
|
|
|
|
^ |
Pearson's r significant at the 0.10 level. |
|
|
||
|
* |
Pearson's r significant at the 0.05 level. |
|
|
||
|
** |
Pearson's r significant at the 0.01 level. |
|
|
||
Table 2: Regional correlations between city and empire
sizes
One problem with the bivariate results in Table 2
is that they may be due to the secular trends in which both cities and empires
increase in size over the long run rather than to medium-term oscillations.[9]
We are most interested in the medium term relations between cities and empires
here.
There are two ways to remove the effects of the
secular upward trend. The first is to compute partial correlations controlling
for time. These results are presented in Table 2. Another method of detrending
is to compute first differences -- the change scores from one period to the
next. The irregular (and infrequent) time points of the early city size
estimates make change score detrending complicated because the changes must be
weighted by the amount of time that elapses between estimate intervals. We have
examined the regional correlations among change scores for empire and city
growth and found mixed results that only partly confirm our analysis using the
partial correlation method of detrending. We think this discrepancy may be due
to small variations in time lags that lower the correlations among change
scores. Examination of the graphs presented in this paper shows that, while cities
and empires tend to grow and decline in the same overall periods, sometimes it
is cities that lead and sometimes empires. These changes reduce the
correlations between simultaneous change scores, but the general middle-run
positive relationships are revealed in the partial correlations. More research
is needed to sort this out, but we contend that it makes sense to wait until we
have better estimates rather than flogging the existing poor data.
The detrended partial correlations in Table 2 show
that there are important differences among regions in the relationships between
city and empire sizes. The biggest difference between the bivariate and
detrended partial correlations are in the East Asian and West Asian regions.
The rather substantial and statistically significant East Asian bivariate
correlation of .61 drops to -.19 when the long-term trend is taken out by means
of controlling for year. The West Asian correlation drops from .54 to .21. Another difference is that the
relationship in Mesopotamia is reduced from .69 to .49. The South Asian
correlation also decreased, but it was already low and insignificant. So only
Europe, West Asia and Mesopotamia show a rather substantial positive
relationship between size and power once the long-term trend is controlled.
South Asia, East Asia and Egypt do not have medium term temporal correlations
between city sizes and empire sizes.
So we find important differences across regions.
It is likely that the relationship between urbanization and political power
varies over time (more below), and because of geographical, climatic and other
differences across regions.
The high correlation between the
medium-run size of the largest empire and the size of the largest city in
Europe would seem to fly in the face of the usual notions about how Europe
differs from the other regions. It is usually thought that the rise of
capitalism in Europe led to the emergence of large cities based on economic
power and trade centrality rather than the building of imperial capitals based on
the ability to extract tribute. This might produce a lower rather than a higher
temporal correlation between empires and city sizes in Europe. Looking at exactly which empires and which
cities were the largest enables us to know whether or not the largest cities
were the capitals of the largest empires, or alternatively whether there might
be regional growth-decline phases in which both cities and empires expand and
contract together despite not being directly linked. Figures 5 – 7 (below) help
us to sort this out.
Figure
5: Largest Cities and Empires in Mesopotamia
Table 1
(above) is also helpful for discerning what is going on in the Mesopotamian
region. Figure 5 starts in 2800 BCE. The largest city in 1800 BCE was Mari of
the Amorite state, while Taagepera tells us that the Old Assyrian state was the
largest in the region at this time. It’s capital, Ashur, was not the largest
city. The Babylonian empire conquered Mari in 1700 BCE and the city of Babylon
was then the largest in the region. The Hittite Empire was large in 1360 BC and
so was its capital, Khattushash (Hattusa). But the Neo-Assyrian Empire grew
larger than the Hittite after 1350, while Hattusa remained the largest city,
until the Hittite state again became largest in 1200. Then the Babylonia Empire
and Babylon surpass all from 1050 to 900. Calah (Nimrud) was Ashurnasirpal II’s
capital of the Assyrian Empire before the building of Nineveh, so the match
between city and empire is again direct from 850 to 650.
Figure 6: West Asian Largest Cities and Empires
Examination of Figure 6 shows that indeed there is
usually a direct connection between the largest city and the largest empire in
West Asia, but there are a few exceptions in addition to those already pointed
out in Mesopotamia. The Achaemenid
Persian Empire did not create a new city larger than those it conquered, and so
Babylon remained the largest city during the Persian expansion. The Alexandrian
conquest led to the founding of Seleucia, which was then the largest city. The
Sassanian Empire built Ctesiphon near in the old heartland of Mesopotamia. And
the rise of Islam eventually created Baghdad in the same region. After the
decline of Baghdad there was a period in which Byzantine Constantinople was
larger than any of the cities of the fragmented Islamic caliphates. So the positive correlation in the West
Asian region between city and empire sizes is both direct (a large empire
created a large city) and indirect in that periods in which there were large cities
tended to be periods in which there were large empires despite only an indirect
connection.
Figure 7: Largest Cities and Empires in Europe
The same kind of comparison for the region of
Europe produces a somewhat different result (see Figure 7). In Europe there is
also a rather high partial correlation between largest empire and largest city
(.73). And the period between 430 BCE and 850 CE shows the same kind of
relationship that we saw in West Asia, where the capital of the largest empire
is most of the time the largest city in the region. But in Europe we see a
radical divergence from this situation after 850 CE, in which the largest city
was virtually never located in the largest empire, but there was nevertheless a
positive relationship between the growth/decline phases of cities and empires.
The reason for this is not too hard to discover.
Europe developed a new form of imperialism in which relatively small European
nation-states like Portugal, Spain, the Netherlands, France and England were
conquering distant colonial empires in the Americas, Africa and Asia. These
were large empires, and the resultant extracted riches supported the growth of
the largest cities in Europe, but these colonial empires were not in Europe.
Rather the largest states in Europe, as indicated by territorial size, were the
Ottoman Empire and Russia. Actually if we had included Constantinople, capital
of the Ottoman Empire, in our list of “European” cities then it would have been
the largest city until 1800. But even
with Constantinople excluded and the emergence of the colonial empires there is
a positive relationship between growth/decline phases of largest cities and
states in Europe. This is because the whole region went through waves of economic
growth and state expansion, earlier versions of the great waves of
globalization seen in the nineteenth and twentieth centuries.
We also want to examine the relationships between
polity size and city size within particular empires, but unfortunately we do
not yet have enough data on city sizes within empires to make possible the
calculation of meaningful correlations. Our examination of modern colonial
empires looking at the territorial size of the empire and the population size
of the capital city (e.g the French Empire and Paris; the British Empire and
London) revealed unsurprising positive correlations and significant partial
correlations despite the collapse of the colonial empires resulting from
twentieth century decolonization.[10]
When we use PMNs (expanding networks
of polities that ally and make war with one another) as the unit of analysis we
find results that are quite similar to those shown in Table 2. The expanding
Central PMN that began with the merger of the Mesopotamian and Egyptian PMNs in
1520 BCE reveals a bivariate correlation of .83 and a partial correlation of
.59 for the period from 1500 BCE to 1990 CE. The Indic and East Asian PMNs show
little or no correlation between largest cities and largest empires. We will
return to the discussion of why this should be the case in our conclusions
below.
Regional Waves of Growth and Decline
Our examination of the relationships among size
distributions of cities and polities did not reveal any significant
associations,[11] but our
correlations between the sizes of largest and second largest cities and empires
produced a rather fascinating finding. Do largest and second largest cities
grow and decline in the same periods, or does the growth of one city result in
the decline of adjacent large cities? In other words, is city growth a zero-sum
game or are there regional boom and bust periods that affect the sizes of
larger and smaller cities synchronously? And we may ask the same question of
empires. Earlier work indicated (Chase-Dunn, Manning and Hall 2000) that
empires tend to grow contemporaneously – periods in which the largest empire is
growing tend also to be periods in which the second largest empire in growing
in the same region. This would seem to be counter-intuitive, and bears further
examination of both empire and city growth decline sequences.
Table 3 shows partial correlations (controlling
for the long-term trend) between the largest and the second largest cities in
each of our six regions.
|
|
Correlations
between 3-period moving average of largest and second largest cities |
||||
|
|
|
|
|
|
|
|
|
Region |
Bivariate r |
Partial r |
Biv. N |
Years |
|
|
East Asia |
0.888** |
0.629** |
31 |
1360 B.C.E. - 1800
C.E. |
|
|
West Asia |
0.968** |
0.947** |
46 |
2800 B.C.E. - 1500
C.E. |
|
|
Europe |
0.524** |
0.611** |
24 |
430 B.C.E. - 1800
C.E. |
|
|
South Asia |
0.605** |
0.608^ |
9 |
200 B.C.E. - 1500
C.E. |
|
|
|
|
|
|
|
|
^ |
Pearson's r significant at the 0.10 level. |
|
|
||
|
* |
Pearson's r significant at the 0.05 level. |
|
|
||
|
** |
Pearson's r significant at the 0.01 level. |
|
|
||
Table 3: Temporal correlations among largest and second largest cities
The results in Table 3 are
significant evidence that regions experience oscillations of growth and decline
periods in which both largest and second largest cities expand and then later
decline. Except for South Asia, where we have only nine time points with
information on the sizes of the two largest cities, all the other regions have
statistically significant positive temporal correlations between city growth
even after the long-term trend is removed. This is strong evidence against the
idea that expansion of cities is a zero-sum game in which a growing city takes
resources or territory from adjacent cities. Rather it must be processes of
growth and expansion occurring synchronously within regions, as well as periods
of regional contraction, that account for these relationships.
|
Region |
Period |
Partial Correlation
between largest and second largest empires |
|
Egypt |
2300
BCE- 550 BCE |
.438** |
|
Mesopotamia |
2800
BCE – 550 BCE |
.934** |
|
East
Asia |
1360
BCE- 1800 CE |
.662** |
|
Europe |
430
BCE – 1800 CE |
.882** |
|
West
Asia |
2000
BCE – 1500 CE |
.239** |
** Significant at the .01 level
Table 4: Partial correlations for largest and second largest empires controlling for year
Table 4 shows that a similar pattern of growth and
decline periods operates when we examine changes in the sizes of the largest
and second largest empires. We do not have enough data to examine this
relationship for South Asia. But all the other regions show that empires grow
and decline in the same periods. This is even more amazing than the results for
cities because we know that some empire growth is at the expense of neighboring
empires. The regional expansion and contraction phases must be strong enough to
overcome this negative effect.
We can get a better idea about how
this may be working by examining which cities and empires are growing when.
Figure 8 (below) shows the sizes of the largest and second largest cities in
East Asia.
Figure
8: Largest and Second Largest Cities in East Asia
One relevant consideration about these results
that should be noted is that individual cities and empires change position when
the second largest passes the largest in size. Because we are looking at ranks
rather than at individual cities the resulting correlations may be somewhat
larger. But Figure 8 shows that the notion of regional growth/decline phases is
substantiated except for the early seventeenth century CE when Peking declined
while the second largest city Yedo (Tokyo) was growing.[12]
The notion of cities growing and declining in
complementary phases is less difficult to accept than the idea that the
territorial sizes of empires are non-zero sum. We know that tributary states
vie with each other for border regions, so how is it possible that largest and
second largest empires grow and decline together over time? Let us again
examine the East Asia region, except now we will look at the empires.
Figure 9: Largest and Second Largest Empires in East Asia
The partial correlation for largest and second
largest empires is statistically significant but we can see several instances
in Figure 9 in which a zero-sum interaction between competing states appears.
The interaction between the Western Han and the Huns is an obvious example, and
a less dramatic but similar negative interaction appears between the Tang and
the Tufan. The graph ends before the emergence of the Mongol Empire because its
huge size would drown all earlier variation. [13]
Conclusions
This study of cities and empires is necessarily
inconclusive because of the incomplete and unreliable nature of the data that
we have on city sizes and the territorial sizes of empires. Only a strong
effort to improve the existing data sets will remedy this. But we suspect that
most of the findings reported above will be confirmed once we have better data.
We expect that future research will continue to find important differences
among regions with respect to the temporality of city and empire growth/decline
phases. And we also expect that within regions there will be period differences
because of changes in the relationship between demography, economic
institutions and techniques of power.
We have used intersocietal regions
as the unit of analysis in this chapter. A different approach would be to study
individual empires and their cities. Because of missing data we have only been
able to do this for two states – England and France. These results for these
two countries are reported in Appendix B [14]
and were discussed above.
One important finding is the
significant positive medium-run temporal associations between city sizes and
empire sizes in Europe and West Asia, and a smaller positive relationship in
Mesopotamia. These contrast with very small correlations in South Asia, Egypt
and East Asia. We do not have a good comprehensive explanation for this pattern
of regional differences. The examination of which cities and which empires are
growing and declining together in Mesopotamia, West Asia and Europe suggests
that the positive medium-term temporal relationship is partly due to the fact
that most expanding empires build large capital cities and partly due to the
periodic nature of regional growth/decline phases that affect both cities and
empires. But why do these same factors not produce positive medium-run
relationships between city and empire sizes in Egypt, South Asia and East Asia?
Egyptian cities tended to be
monumental centers rather than residential centers, so population sizes of
cities may be a poor reflection of the actions of states. East Asia, despite
much recent emphasis on similarities with Europe rather than the differences,
was more centralized more of the time than other regions. But this should
strengthen the relationship between empire and large cities. Figure 9 (above)
suggests a different explanation for the low temporal association between large
cities and large empires in East Asia. Many of the very largest Asian empires
in terms of territorial size were the huge confederations put together by
nomadic conquerors from the Central Asian steppes (the Hsiung-nu (Huns), the
Turks (Wigur), Tufan and the Mongols. These horse-riding nomads were notorious
in their disdain for cities and city life, and so they rarely used the fruits
of conquest to erect large urban centers.
The other big finding is the
non-zero sum nature of the relationships between largest and second largest
cities and empires in Egypt, Mesopotamia, East Asia, West Asia and
Europe. For South Asia we do not have much data on second largest cities or
empires. These results strongly indicate that regions go through periods of
growth in which both the largest and the second largest cities (ditto empires)
are growing followed by periods of decline in which these are declining
together. This is especially surprising in the case of the territorial sizes of
empires because we know that contending empires fight with each other over
border areas and sometimes one conquers another and incorporates its territory.
Though we do find instances of this kind of zero-sum interaction in the graphs,[15]
the overall relationship is positive even when the long-term trend is taken out
by computing a partial correlation that controls for time. This supports the
notion that regional interaction networks were behaving systemically. Our
tentative results support the idea that it is the development of economic and
political interaction networks as well as the emergence of new techniques of
power that have been the major factors in the relationships between territorial
power and demographic size.
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Endnotes