Realism and World Politics

represents one end of a spectrum. At the other end lies ‘empire’ where independent
communities are directly administered from an imperial centre. As the pendulum
moves away from anarchy, communities increasingly come under the control of a
dominant power. Within hegemony, for example, communities can no longer
pursue independent foreign policies. From Watson’s perspective, history cannot be
characterized in terms of a predetermined and regular movement from anarchy to
empire. On the contrary, empire and anarchy represent extreme positions and for
most of world history, communities have operated between the ends of the spectrum
because systemic pressures push the pendulum away from the extremes and, as a
consequence, there is a significant tendency for the pendulum to move to the lowest
point in its swing.
Watson’s pendulum model problematizes Waltz’s assessment of polarity. But as
the earlier discussion on units foreshadowed, Waltz’s theory is also unable to accom-
modate the idea of structurally differentiated units and the idea of heterogeneous
systems. His approach to structure makes it impossible to engage with the structural
differentiation of units, and yet world history not only demonstrates that hetero-
geneous systems are a very common feature of world history but also that the
structural differentiation of units inevitably has an impact on the interaction between
units. This factor is very apparent in the case of hegemonic systems. The Roman
Empire, for example, had to interact with empires in the east and tribes in the west
and the resulting patterns of behaviour were very different.^28 By the same token,
the Chinese had to deal with nomadic tribes in the north and centralized states in
the south. In the north, war was endemic, whereas in the south it was almost
completely absent.^29 From Waltz’s perspective, of course, if these empires do
represent examples of systems, then they are systems that operate in the absence of
a structure. In a previous discussion of this issue we established a typology of
international systems that embraced the structural and functional differentiation of
units. This typology illustrates that world history demonstrates a complexity that
simply cannot be accommodated by Waltz’s theoretical framework.

The paradox of parsimony 295

Medieval

systems

Republicansystems

EU-typeunions

STRUCTURALLY

DIFFERENTIATED

STRUCTURALLY

UNDIFFERENTIATED

Classical systemsof

heterogenous

autonomous units

FUNCTIONALLY

DIFFERENTIATED

FUNCTIONALLY

UNDIFFERENTIATED

PureWalzian

Westphallian systems

oflikeunits

Figure 17.3Types of international system: linking structural and functional
differentiation^30