Looking back on the recent Second Russo-Ukrainian War and Putin's annexation of the Donbass, here's a fun WI.
What would have happened if the Great Powers decided that territorial borders should remain relatively fixed, with only independence/unification/minor readjustments allowed, at the end of WW2? So victory in war would no longer be a justification for territorial annexations.
I suppose Israel wouldn't have been allowed to annex the Golan Heights, for example.