Virginia Postrel on the American Empire:
A 21st-century representative democracy with a large regulatory bureaucracy and many overseas involvements may be problematic. But it isn't an "empire" unless that term just means "a government I don't like."
There's more. As always with Virginia's stuff, just start at the top and keep reading until you're into reruns.
We'd have one pretty sweet empire if we followed the rule, "where our troops go, our troops stay". (Rome, Soviet Union, etc)
Let's just say we started after WWII and acted like the Soviet Union did. US States 51-100 would include parts of: France, Germany, Italy, Algeria, Tunisia, Morocco, Libya, Netherlands, Belgium, Japan, Phillipines, pretty much the entire Pacific excluding Australia, South Korea, Bosnia, Southern Iraq, Kuwait, Haiti, Panama, Grenada, and Afghanistan.
Do we own ANY of this today? All we really want is for the rest of the world to get their crap together and let us practice our representative democracy in peace.