Since the Soviet Union collapsed almost two and a half decades ago, the United States has enjoyed unparalleled power in the international system. U.S. preponderance is particularly marked in the military realm. The United States is the only country whose military has a global “defense” perimeter. In Pentagon-speak, Central Command is not in charge of defending the territory around Lebanon, Kansas, the geographic center of the contiguous forty-eight United States. Rather, it is in charge of maintaining – and, if necessary, creating – conditions that Washington considers secure in the Middle East, North Africa, and Central Asia. To promote security on a global scale, the U.S. military maintains or has access to more than 1,000 facilities scattered over more than 140 countries, in which more than 200,000 U.S. military personnel are stationed. In their leisure time, they can enjoy one of the 234 golf courses the Pentagon runs around the world.

No other state in modern history has enjoyed this sort of power preponderance. At the end of the nineteenth century, for instance, Britain was the most powerful state in the world. In the era when global power projection relied mostly on naval forces, British strategists developed a yardstick to guarantee Britain's edge: the Royal Navy had to remain as powerful as the two next-largest navies combined. Today, eighteen countries operate blue-water war fleets. The U.S. Navy fleet is larger than all the other seventeen combined.