Many of the mathematicians, especially those of Jewish background, fled this southeastern part of Poland in 1941 when it became clear that it would be invaded by Germany. Few of the mathematicians survived World War II, but after the war a group including some of the original community carried on their work in western Poland's Wrocław, the successor city to prewar Lwów; see Polish population transfers (1944–1946). A number of the prewar mathematicians, prominent among them Stanisław Ulam, became famous for work done in the West.