I instinctively reject the idea that the Soviet Union and America are empires—“the evil empire” and “the American empire”. At one level, this makes no sense: if we say an empire is a country that occupies and administers other countries, then both count. However, there is a difference: the difference is that both are democracies, whereas a traditional empire is aristocratic. The difference is that an empire, the Roman Empire, would conquer a province and send a man to administer it—he was the government; perhaps he negotiated with locals, tolerated certain religions and practices, but mainly he was there to enforce the law and secure the trade routes.
The difference with “democratic empires” is that the occupied population—segments of it—meets the imperial centre halfway and enjoys a collegiate “little brother” relationship with the centre. Hence, for example, East Germany was not “run” by the USSR; they copied the USSR carefully, but the German Communists genuinely believed they were in a collaborative arrangement, albeit as juniors, with the USSR (both wanted world social revolution, an end to reactionary ideas and practices). The Soviet embassy might have vetoed, in an indirect way, certain East Communist ideas but East Germany was not “ruled from the Soviet embassy” as with an imperial governor.
A similar situation pertains to, say, Britain. If Corbyn became PM, sought to leave NATO as he has always wanted, the US wouldn’t directly oppose this move from their huge embassy; they might work to stall it through delaying tactics, augmented by CIA agents and people who genuinely believe in “Enlightenment values”—as British through, say, David Hume, as Karl Marx was German. What would not happen is for some lackey to run to the US embassy to say, “Governor, a ferocious bearded tribe from the North, the Corbynii, have occupied Parliament—call out the legions.” Yet it is also true that Britain and, anachronistically, East Germany do not exercise genuine sovereignty—the crux is that democratic empires value beliefs.