Is America fighting for its empire?

Today my Archaeology teacher was talking about how every empire eventually completely caves in upon itself in one form or another, and I began to entertain the possibility that through all the protesting, arguing, and disagreement- perhaps the United States is acting accordingly.

If you consider what it will be like reading about the US 200 years from now, will its fall be that big of a surprise? The writing has been all over the wall since the 50s, and has riddled major media since the 80s.

So; is America justified in its actions to defend the empire, even if they don't come to truthful terms with them (has anyone ever?)

With open markets and free trade in the modern world, you don't need to control extensive territory anymore; information and capital are better at controlling resources than the military alternative.

As with >>4 the definition refers to physical territory, and thus a nation with an agenda of geographic expansion will be Imperial in nature.

Has America an imperial agenda? I think it does. Because of the huge amount of money spent on the military it needs to have return of the investment.