Read Paul Kennedy's "The Rise and Fall of the Great Powers".
An economically expanding power… may well prefer to become rich rather than to spend heavily on armaments. A half-century later, priorities may well have altered. The earlier economic expansion has brought with it overseas obligations (dependence upon foreign markets and raw materials, military alliances, perhaps bases and colonies)…. In these more troubled circumstances, the Great Power is likely to find itself spending much more on defense than it did two generations earlier, and yet still discover that the world is a less secure environment—simply because other powers have grown faster, and are becoming stronger…. Great Powers in relative decline instinctively respond by spending more on ‘security,’ and thereby divert potential resources from ‘investment’ and compound their long-term dilemma (emphasis added).I believe, along with Chalmers Johnson (see his Nemesis), that this is the position the U.S. is now in; it is on the downslope of over-reaching militarily which will eventually hurt it economically and seriously undermine its world power.