If the colonial empires existed today, what would you call them?
Orwell wrote an essay on Kipling that applied the label of "pre-fascist" to him so feel free to use that instead. For the sake of conversation we can then agree that anti-pre-fascists are antifa or close enough. You could also insist on pre-antifa, that's pretty catchy.
After all, lesser evil empires fighting fascists still earn the title of antifascist, do they not?
Even if they, say, starve, imprison, and use "forced labor" on millions of their own citizens as a form of political control.
Otherwise you'll find that pretty much the only people that deserve the term of antifa are anarchists, which I'm also fine with, welcome to the right side of socialism.