Might Washington, like Rome, fall victim to imperial overstretch? Could military force abroad eventually have to be withdrawn because of bankruptcy at home? Might the whole idea of America eventually be challenged and destroyed by some charismatic new faith: some fundamentalist variant on Christianity? Or will nature disrupt America's new world order?

As the dynamic of imperial overstretch became clearer, many of the great powers decided to solve their security dilemmas through even bolder preventive offensives. None of these efforts worked. To secure their European holdings, Napoleon and Hitler marched to Moscow, only to be engulfed in the Russian winter. Kaiser Wilhelm's Germany tried to break the allies' encirclement through unrestricted submarine warfare, which brought America's industrial might into the war against it. Imperial Japan, facing a quagmire in China and a U.S. oil embargo, tried to break what it saw as impending encirclement by seizing the Indonesian oil fields and preventively attacking Pearl Harbor. All sought security through expansion, and all ended in imperial collapse.

Although the United States is at present still pre-eminent economically and perhaps even militarily, it cannot avoid the two great tests that challenge the longevity of every major power that occupies the number-one position in world affairs. First, in the military-strategic realm, can it preserve a reasonable balance between the nation's perceived defense commitments and the means it possesses to maintain those commitments? And second, as an intimately related question, can it preserve the technological and economic bases of its power from relative erosion in the face of the ever-shifting patterns of global production? This test of American abilities will be the greater because America, like Imperial Spain around 1600 or the British Empire around 1900, bears a heavy burden of strategic commitments, made decades earlier, when the nation's political, economic, and military capacity to influence world affairs seemed so much more assured. The United States now runs the risk, so familiar to historians of the rise and fall of Great Powers, of what might be called "imperial overstretch": that is to say, decision-makers in Washington must face the awkward and enduring fact that the total of the United States's global interests and obligations is nowadays far too large for the country to be able to defend them all simultaneously.