GWB is known for uninformed hyperbole. How do you quantify it? Over what time period? only current countries known as past empires or old empires allowed too? China can be considered a 4k yr country w/long periods of empire building, which dynasty?. When I think old world colonizers, I don't even think England as I find the Spanish and Portuguese much more brutal in their conquest. The Spanish by and large wiped out natives unintentionally but w/o much care either through disease. Does that death count "count" since it was not intentional? Do we consider the death rate in our estimate? Death as ratio of population (I wouldn't think so)?
Russia's "ocean" to their colonies was on land and a lot of the brutality remains suppressed or has been lost or unrecorded.
FWIW, first thing that came to mind was Ghengis Khan, Spanish, Roman