And... What belonged to who is quite close to meaningless. When do you want to set the date of the original ownership? Some 35 000 years ago when these lands were probably first settled or at some arbitrary point later on? How do you treat the right to self-determination and regions of mixed ethnicity with no absolute majority?
Lands of current Belarus and Ukraine belonged to Polish–Lithuanian Commonwealth before partitions, then they belonged mostly to Russia. After the first World War, we ended up in a very complex situation with vast regions with populations of mixed ethnicity and conflicting claims that resulted in wars. Poland claimed these lands as did Lithuania, Belarus, and Ukraine based on the wave of the modern ideas of a nation state. Poland managed to overpower them and focused on Polish–Lithuanian Commonwealth as the original ownership.
https://en.wikipedia.org/wiki/Western_Krai
The idea of state ownership of land has really no absolute truth to it. There are no rules that will allow fairly dividing Africa after what was done to that continent during colonialism, Middle East including Palestine or central and eastern Europe. Well, even dealing with Brexit is quite an impossible task.
Sometimes when reading discussions, I think that some westerners forget that the Soviet Union assaulted Poland 17 days after Germans attacked us.
So to remind everyone, Soviets started the whole bloody Second World War!
Not to mention, that after they crashed Poland they killed 22 000 Polish captives by shutting them in the back of their head in an effort to eradicate Polish culture. https://en.wikipedia.org/wiki/Katyn_massacre
Russians did not fully admit this crime until freaking 2010. These liars were either denying it or blaming this crime on Germans while they had documents clearly stating orders.
They assaulted Poland in 1939, and they were assaulting us in 1944. They were waiting for Warsaw Uprising to fall, they were preventing western forces to help the uprising. Then they proceeded to effectively occupy Poland till 1989.
Even today if we discuss historical events some Russians will tend to get upset that we are not grateful for the sacrifices of the Red Army. But they were not liberating us. They were raping, pillaging and brutally crashing anyone who dared to think.
Putting any moral equality between western participation in World War II and Soviets is just wrong!