The region only became part of the Soviet Union under the terms of the Molotov–Ribbentrop Pact in 1939, when it was annexed to the Ukrainian SSR. It was occupied by Nazi Germany from 1941 to 1944, when almost all local Jews were killed, and remained in Soviet hands after World War II as was arranged during the Teheran and Yalta conferences. Local Poles were expelled and Ukrainians expelled from Poland arrived. Given its historical development, Lviv Oblast is one of the least Russified and Sovietized parts of Ukraine, with much of its Polish and Habsburg heritage still visible today.