No country in modern history has possessed as much global military power as the United States. Yet some analysts now argue that the US is following in the footsteps of the United Kingdom, the last global hegemon to decline. This historical analogy, though increasingly popular, is misleading.

Britain was never as dominant as the US is today. To be sure, it maintained a navy equal in size to the next two fleets combined, and its empire, on which the sun never set, ruled over a quarter of humankind. But there were major differences in the relative power resources of imperial Britain and contemporary America. By the outbreak of World War I, Britain ranked only fourth among the great powers in terms of military personnel, fourth in terms of GDP, and third in military spending.

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