Complicated. UK for example claims to have gotten permission from the Ottoman Turks to take a lot of stuff from Greece. At that time, Turks were the legit ruler

Complicated. UK for example claims to have gotten permission from the Ottoman Turks to take a lot of stuff from Greece. At that time, Turks were the legit rulers, as Greece didn;t exist, so are they stolen? Also, many time the Nazis officially or unofficially (ruling elites in city) "bought" them from Jewish owners. We can guess the price "agreed" to in those times.