Three decades ago, the radical left used the term "American empire" as an epithet. Now that same term has come out of the closet: analysts on both the left and right now use it to explain - if not guide - American foreign policy.
In many ways, the metaphor of empire is seductive. The American military has a global reach, with bases around the world, and its regional commanders sometimes act like proconsuls. English is a lingua franca like Latin. The US economy is the largest in the world, and American culture serves as a magnet. But it is a mistake to confuse primacy with empire.
The US is certainly not an empire in the way we think of the European empires of the 19th and 20th centuries, because the core feature of that imperialism was political power. Although unequal relationships between the US and weaker powers certainly exist and can be conducive to exploitation, the term "imperial" is not only inaccurate but misleading in the absence of formal political control.
To be sure, the US now has more power resources relative to other countries than Britain had at its imperial peak. But the US has less power - in the sense of control over other countries' internal behavior - than Britain did when it ruled a quarter of the globe.