Power and the Varieties of Order - Liberal Leviathan: The Origins, Crisis, and Transformation of the American World Order - page 29

by the United States and the Soviet Union. The power structure became unipolar in the 1990s
with the collapse of the Soviet Union and the continuing growth of America's material cap-
abilities relative to the other major states.
These broad differences in the international distribution of power are captured in aggreg-
ate measures that combine economic and military size. These percentage indicators provide
measures of both economic capacity and military might. The gross national income (GNI)
measure—particularly utilizing measures of both aggregate and per capita GNI—provides
the single best measure of power capabilities. 4 In contrast, military spending captures effort,
not potential. 5 The multipolarity of the earlier periods is contrasted with the bipolarity of the
Cold War and the unipolarity of the last two decades. (See figure 2-1 . )
These measures of aggregate power show the distinctiveness of the postwar era of bipolar-
ity and the last two decades of unipolarity. In previous centuries, power was shared more or
less evenly among a group of great powers. Leading states were only slightly set apart from
the other great powers. Moreover, in these earlier periods the leading states were either great
commercial and naval powers or great military powers on land, but they were never both.
Great Britain emerged as the leading economic and naval power in the nineteenth century,
but other major states matched or exceeded British capabilities in some areas. As Brooks and
Wohlforth observe, “[e]ven at the height of the Pax Britannica, the United Kingdom was out-
spent, outmanned, and outgunned by both France and Russia.” 6 Similarly, the United States
emerged from World War II as the world's leading economy, and it was unrivaled in many
areas of military power, including air and naval capabilities. But during the Cold War, the
Soviet Union matched the United States in overall military capabilities, reinforced by its vast
territorial holdings and military investments. During the Cold War, the United States and the
Soviet Union were both poles in a geopolitically divided world.
Figure 2-1: Distribution (Percentage) of Economic and Military Capabilities among the Major Powers a
(17th-21st Centuries)