A colonial empire is a collective of territories (often called colonies), either contiguous with the imperial center or located overseas, settled by the population of a certain state and governed by that state.
The empire and later the USSR conquered a lot of land, but that was contiguous.
BTW I only chimed in like that because people routinely cite, for example, casualty figures ("Ukraine has 1M+ dead") intended to make the situation look much worse for Ukraine than it actually is (and to apparently suggest that there's a giant conspiracy to keep keep the truth hidden from us). Turns out they're invariably skimming, looking at a random figure they saw (for example an article claiming 1M total casualties included wounded, and on both sides, meaning mostly Russian), and duly misremembering in a specific way that happens to align with the narratives they like.
So this case it turns out I was wrong (but at least in an interpretive way; I didn't think about how the definition of "refugee" is overly specific and doesn't really count the number of people forced to leave the country).
On that note, if you have your own estimate of the current numbers for military / civilian fatalities, that would be of interest also.