Power and Size:
Urbanization and
Empire Formation in World-Systems
Christopher Chase-Dunn
Alexis Alvarez
Daniel Pasciuti
Institute for Research on World-Systems
University of
California, Riverside
V 9-2-03 (7699 words)
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 world regions. 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? World-systems are
intersocietal interaction networks in which culturally different peoples are
strongly linked together by trade, political-military engagement and
information flows.
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.[1]
Chase-Dunn and Willard (1993) examined urban growth and
city-size distributions in nine different regional political/military networks
(PMNs) [2]
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 was related to changes in the degree of political integration and
the centralization of state power. 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 about 650 BCE to about 1500
CE.[3]
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 synchronicities 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 synchrony phenomenon using constant regions, and so this phenomenon 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 warriors to contested regions. The winner of a confrontation is that
group that can bring the larger number of warriors 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.
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). 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 Eurasia
(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 cut away the general observation of a correlation between power and
demographic size. What it shows 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 city 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. These observations suggest that we
should try to overcome the difficulties encountered in studying the last two
centuries in order to shed more light on the power-size relationship.[4]
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. Our units of analysis will be:
- Political/Military Networks (PMNs), otherwise
called interstate systems;
- Constant Regions[5],
in order to see how spatial boundaries might be related to patterns in the
city-empire relationship; and
- 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.
And
we will examine the temporal relations between the simple sizes of cities and
empires, as well as size distributions of cities and the size of 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. 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.
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. 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 of men 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. A new project to improve upon Chandler’s compendium 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.[6]
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 (square
megameters x10) |
Empire Name |
City Size
(thousands) |
City Name |
|
-2800 |
1 |
Kish |
80 |
Uruk* |
|
-2500 |
3 |
Kish |
50 |
Uruk* |
|
-2400 |
5 |
Lagash |
|
|
|
-2300 |
65 |
Akkadian |
36 |
Agade*# |
|
-2200 |
25 |
Akkadian |
|
|
|
-2100 |
3 |
Ur |
|
|
|
-2000 |
10 |
Sumer |
65 |
Ur |
|
-1900 |
0 |
|
|
|
|
-1800 |
10 |
Old Assyria |
29 |
Mari |
|
-1700 |
25 |
Babylon |
|
|
|
-1600 |
16.6 |
Babylon |
60 |
Babylon |
|
-1500 |
10 |
Kassite |
|
|
|
-1450 |
10 |
Kassite |
|
|
|
-1400 |
10 |
Kassite |
|
|
|
-1360 |
21.7 |
Hittites |
45 |
Khattushash
(Hattusa) |
|
-1350 |
5 |
Assyria |
45 |
Khattushash
(Hattusa) |
|
-1300 |
10 |
Assyria |
|
|
|
-1250 |
15 |
Assyria |
|
|
|
-1200 |
25 |
Hittites |
48 |
Khattushash
(Hattusa) |
|
-1150 |
5 |
Assyria |
|
|
|
-1100 |
40 |
Assyria |
|
|
|
-1050 |
15 |
Babylon |
|
|
|
-1000 |
15 |
Babylon |
51 |
Babylon |
|
-950 |
15 |
Babylon |
|
|
|
-900 |
15 |
Babylon |
|
|
|
-850 |
40 |
Assyria |
|
|
|
-800 |
57.9 |
Assyria |
50 |
Calah |
|
-750 |
40 |
Assyria |
|
|
|
-700 |
90 |
Assyria |
|
|
|
-650 |
93.3 |
Assyria |
120 |
Nineveh |
|
-600 |
25 |
Babylon |
|
|
|
-550 |
50 |
Babylon |
|
|
Table 1:Mesopotamian Largest Empires and Cities
*These estimates are
from Modelski (1997). 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 1 and
2; every 10 years for the other regions in Table 2 and the figures in Appendix
A, see http://www.irows.ucr.edu/research/citemp/isa02/isa02.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 2: 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 2). 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 3.
Figure 3: 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 four of the six regions have
statistically significant positive bivariate correlations between city and
empire sizes (Column 2). 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.
Table 2:
Regional correlations between city and empire sizes
One
problem with the bivariate results in Column Two of Table 2 is that the positive
correlations may be due to the secular trends rather than to medium-term
oscillations. Both city and empire sizes increase over the long run.[7]
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 Column 3 of Table 2. Another method of detrending would 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 messy, so this should only be done after more regular intervals of
measurement have been established.
The
detrended partial correlations in Column Three of Table 2 show that there are
important differences among regions with respect to the relationship between
city and empire sizes. The main difference between the bivariate and detrended
partial correlations is in the East Asian region. The rather substantial and
statistically significant East Asian bivariate correlation of .47 drops to .12
when the long-term trend is taken out. Another difference is that the
relationship in Mesopotamia is reduced from .45 to .30. The South Asian
correlation also decreased, but it was already low and insignificant. So Europe
and West Asia show a rather substantial positive relationship between size and
power and Mesopotamia has a nearly significant positive relationship. 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 4-6 (below) help us to sort
this out.
Figure
4: Largest Cities and Empires in Mesopotamia
Table 1 (above) is also helpful for
discerning what is going on in the Mesopotamian region. Figure 4 starts in 2000
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, Assur, 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 5: West Asian Largest Cities and Empires
Examination of Figure 5 shows that indeed there is
usually a direct connection between the largest city and the largest empire,
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 6: Largest Cities and Empires in Europe
The same kind of comparison for the region of
Europe produces a somewhat different result (see Figure 6). In Europe there is
also a rather high partial correlation between largest empire and largest city
(.88). 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 is a geographical region
that 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.[8]
When we use PMNs (expanding networks of polities that
ally and make war with one another), we find results that are quite similar to
those shown in Table 2. The expanding Central PMN that begins with the merger
of the Mesopotamian and Egyptian PMNs in 1500 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, 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, and largest and second largest empires
in each of our six regions for the same time periods used in Table 2. The number of time points is reduced in some
cases where we do not have data on second largest cities or empires, and there
are not enough South Asian second empires to compute a correlation for that
region.
Table 3:
Temporal correlations among largest and second largest cities and empires
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 and empires expand and then later decline.
Except for South Asia, where we have only a paucity of data, all the other
regions have statistically significant positive temporal correlations between
city growth (and empire growth) even after the long-term trend is removed. This
is strong evidence against the idea that expansion of cities and empires is a
zero-sum game in which a growing city or empire takes resources or territory
from adjacent cities or empires. 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.
We can get a better idea about how this may be working by
examining which cities and empires are growing when. Figure 7 (below) shows the
largest and second largest cities in East Asia.
Figure 7 : 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 7 shows that the notion of regional growth decline phases is
substantiated except for the early seventeenth century CE when Peking declines
while the second largest city Yedo (Tokyo) is growing.[9] 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 8: 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 8 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. [10]
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 [11]
and were discussed above. More concentrated analysis will allow us to examine
the sizes of more cities within polities and to consider more carefully the
historical events and interactions among polities and regions.
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
East/West 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 8 (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[12],
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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