A piece of Nazi plunder is in the news. I've always wondered: How did the Nazis manage to loot "upwards 20% of the art of Europe" and how much effort was made to return the art to its rightful owners after the war?

by 82364

I've read in news stories that some of the victims' claims to their art was voided after the war because there were too many trades and sales to be undone... but was art trading really that frequent and far-reaching in 1939-1944/5 Europe?