An empire usually has foreign colonies historically speaking and the United States has none. Except for a brief 20 year period when the United States had the Philippines as a colony as a result of the Spanish-American war, before it gave that nation independence. The U.S.A. never did have colonies nor an emperor or imperial government. The original 13 colonies were of course part of the British Empire before the revolution. Today the U.S.A. has a few territories populated by citizens of the U.S.A. in addition to 50 states that became part of the union voluntarily at some point. Puerto Rico is an example; they could petition Congress to become a state yet appear satisfied to be a territory.
There is a plain difference concerning empires and nations historically easy to discern. Britain and Rome had empires as did the Soviet Union in some respects with Warsaw Pact nations taken during the war against the Nazis, yet that definition is debatable. The trouble with morphing historical terms is that they become meaningless in respect to their original sense and one may conflate completely different forms within one form mistakenly. It is as if contemporary history analyst recognize only several ancient forms of government and try to fit new forms into old categories lacking the will to create a new definition for themselves.
Some people like to call the United States an empire because it has a lot of wealth and foreign troops stationed abroad to bring or keep the peace, and one might regard the 1% as an aristocracy, yet technically the United States isn’t an empire so much as a corporatist entity with plutocratic suzerainty that evolved from a national democracy. In this paradigm I would say the 1% act toward the 99% in their own country as suzerains.