During the German-Soviet invasion of Poland in accordance with the secret protocol of Molotov–Ribbentrop Pact, the Soviet forces allied with Nazi Germany invaded eastern Poland on 17 September 1939. As the bulk of the Polish Army was concentrated in the west fighting the Germans "(see also: Polish September Campaign)", the Red Army met with limited resistance and their troops quickly moved westward. Tarnopol was occupied as early as 18 September 1939 without substantial opposition from the Poles, and remained in Soviet hands till Operation Barbarossa. Monuments were destroyed, street names changed, bookshops closed, library collections stolen and transported in lorries to the Russian archives. The province was Sovietized in the atmosphere of terror. Families were deported to Siberia in cattle trains, mainly Polish Christians.