The definition of empire is a group of states or countries ruled by a single supreme authority. All other uses of the term are metaphorical. We can talk about

The definition of empire is a group of states or countries ruled by a single supreme authority. All other uses of the term are metaphorical. We can talk about the McDonald's hamburger empire. When we talk about the American Empire, we're also using the term metaphorically, because think what you will of the US, but it doesn't rule as a supreme authority over anything but a few islands. It may have friends, allies, interests, influence, bargaining power, but it has no subjects, no subjugated peoples. It may have largely founded what is now the world's economic and security order after WWII, but those are all voluntary. The problem is that the overlap between superpower and empire makes the term empire confusing in the American case. "Powerful like an empire" and "an empire" are very different. When we talk or think about the "American Empire", we seek similarities and ignore differences with the Roman Empire, European colonial empires, even the Athenian Empire or Soviet Empire. It makes it sound like the US can tell other countries what to do as it pleases, that the US rules over others. That's a very important mistake, even a dangerous mistake. Allies are not subjects. When a country asks the US military to leave, it leaves. See the Philippines as a good example (and further back as an example of the bad old days, when the US was briefly interested in having a real empire). Today's US is an empire in the sense that Microsoft is an empire -- it is an empire of the willing who can leave whenever they like. And if you can leave whenever you'd like, it's not a real empire.