If you're going to go pre-20th century, Russia has the dubious distinction of having waged the most "total" recorded genocide in history, the Circassian genocide.

Just because you haven't heard of Russia colonizing doesn't mean it didn't happen just as much. It just wasn't where the other imperial empires were. How else would one city come to a rule a continent-sized territory? A big difference is, they didn't keep records of such things. People picture Siberia as an empty wilderness and have no idea that rich societies once lived there.