> The Mongol Empire as an example is still remembered to this day. Nobody cares what exactly they did, but it's common sense that it was pretty bad.

Is it really? I think most people only remember them as successful conquerors.

> British colonial era? Same thing, but half the world still remembers what atrocities they have commited, and it was longer ago as WW I.

Depends! The British Empire lasted until the 1960s -- arguably 1997. That's much fresher than WW1 or WW2.

Besides, who remembers the British concentration camps?