It's true some of it was taken by war. But not nearly as much as the lefties would have you believe. Lewis and Clark went clear across the continent and encountered relatively few settlements.
Besides if the Nazis had won the war the paintings wouldn't now be considered stolen, would they?
The notion that stolen goods if secreted away along enough become the property of the thief is not part of our legal system.
ML/NJ
Call it what you like, it's a scam and wrong.