It’s more than people changing the border to suit them. What suits them is instability, e.g. Iraq where they divide the populations so there is a large Sunni minority whose interests will align with the western powers and will want western help after they are put in power.
Discussion
But that is what the Soviets did, they didn't move people in they moved the Russian borders back and did so for exactly the reason you just gave.
The point is Donbas was always part of Russia it was not colonized. by Russia. As to Crimea though it was part of the strategy but again the real reason and documented as such was Khrushchev's retirement plan.