A variety of theories of international relations and geopolitics have been offered in the course of this century to provide overall framework models for the understanding of conflict and cooperation among nation-states. A century ago, Alfred Thayer Mahan, in The Influence of Seapower Upon History, offered a theory of the mutually reinforcing effects of trade and seapower: Whoever ruled the waves, argued Mahan, ruled the world (Kennedy, 1976, pp. 1-9). Not long thereafter, Sir Halford Mackinder offered a rival theory, that whoever ruled the Eastern European and Central Asian "Heartland" would rule Eurasia, and hence the world (Taylor, 1993, pp. 54-56).
Events through most of the century cast doubts upon both theories. In 1914, Britain had ruled the waves for a century, but it did not rule the world; in dealing with its powerful neighbors across the English Channel it was just one Great Power among several. In that year, a balance of power that operated for a century with relatively little war, and no general coalition war, broke down; two great coalition wars followed in a generation. At the end of the Second World War, Mahan's theory and Mackinder's were poised in a sense directly against one another; the US ruled the waves and the USSR ruled the heartland. Nearly half a century of uneasy bipolar equilibrium followed, ending abruptly in the years around 1990 when the Soviet Union disintegrated -- not from defeat in the global struggle, but from internal collapse.
The current world system is thus, almost by default, a Mahanian one. As American politicians never tire of reminding their constituents, there is only one superpower, the United States, and that superpower is essentially a maritime and commercial state. Britain in its heyday had to struggle to maintain a "two power" standard where the Royal Navy had as many battleships as the next two largest fleets; the United States has more fleet aircraft carriers than...