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?)

Main Entry: em·pire
Pronunciation: 'em-"pIr
Function: noun
Etymology: Middle English, from Old French empire, empirie, from Latin imperium absolute authority, empire, from imperare
1 a (1) : a major political unit having a territory of great extent or a number of territories or peoples under a single sovereign authority; especially : one having an emperor as chief of state (2) : the territory of such a political unit b : something resembling a political empire; especially : an extensive territory or enterprise under single domination or control
2 : imperial sovereignty, rule, or dominion