It's technically not an empire according to the traditional definition, but realistically it is both such a dominating economic and military power in the world that it might as well be an empire without, you know, the colonization and white washing stuff.
The irony is that the leftists, whom often seem to hate this nation, can only safely express their hatred because of the U.S. Constitution and the fact that, through both military might and economic dominance, Russia and Communist China dares not even TRY to conquer the United States. The things that the Political Left hate is what ensures their freedom to safely hate.