Originally Posted by Sulla the Dictator
I would think the opposite, actually. Most Americans are very uncomfortable thinking of us as an "Empire".
But strictly speaking, that is exactly what we have been since the earliest days of the nation. Just within the continental United States. An Empire suggests a variety of distinct peoples or cultures subordinated beneath a single government, as well as a certain scale in terms of territory. The United States has fit both of those categories since the 1840s with the annexation of entire Indian nations under imperium. Then if you count the settling of state sovereignty, you gradually change "states" into "provinces". Then add Alaska, Hawaii, and Puerto Rico, all three foreign possessions with differing ethnic populations and languages annexed and absorbed every bit as much as Cisalpine Gaul.
That's without even arguing the point about client states.
As long as you say, "subordinated beneath a single government" I have no objection to calling the US an empire. Multi-ethnic? Not really. Anglo-Saxon culture absorbed all the other ethnic groups--the melting pot. To non-Americans this is perhaps more obvious than it is to you.
I was thinking mainly in terms of past, truly multi-ethnic empires--the Ottoman Empire, the Austro-Hungarian Empire, to say nothing of the Dutch, the British, the French empires etc. In the contemporary world situation, the US is not by any means an empire in relation to other states. It is simply the military hegemon after the collapse of the (multi-ethnic) Soviet Empire.