That's always been the fundamental problem with anything resembling an "empire", as opposed to a more natural ethnostate, based on tribal affiliation, language, common behaviour/beliefs/"culture" etc. Yes, you can have "minorities", but they have to be willing to think and act like the majority (before the majority can accept "looks don't matter".)

But even a natural ethnostate can become big enough where even those who look and talk alike start to think differently, and want something different, and like a single-celled organism, that society will want to split. The problem comes when there's nowhere for the new behavioural/cultural minority to go, and the majority wants to keep control of the land its got (wars of secession have been seen in both chimps and wolves, and they both ended the same way - with the "rebel faction" being destroyed after trying to claim part of the original pack/troop's territory. Not sure about the chimps (probably Goodall's), but the wolves were from Mech's Isle Royale studies).

Anyway, there's more than one reason behind the increased interest in colonizing space, and the climate change criers of doom are secretly drooling at Antarctica becoming freed-up land ...