In September 1939, during the joint German-Soviet invasion of Poland, which started World War II, Puławy was seized by the Wehrmacht, and afterwards was occupied by Germany. Three German concentration camps operated around Puławy. In 1940 the Germans carried out mass arrests of local Polish intelligentsia, which was then imprisoned in Lublin, and then often deported to concentration camps or murdered in Rury, Lublin. During the occupation, Polish poet Krystyna Krahelska lived in the city from 1940 to 1942 and was part of the Polish underground resistance movement. She is best known as the author of the most popular song of the Polish resistance movement ("Hej chłopcy, bagnet na broń"), which she premiered in 1943 in Warsaw, where she was killed in the Warsaw Uprising in 1944. The town's Jewish population of some 3,600 was first confined to a ghetto, then murdered at the Sobibór camp. The Jewish population ceased to exist and was never reconstituted. The town remained under German occupation until July 25, 1944, when it was freed by the Home Army, as well as the Red Army.