 Before the war Lviv had the third-largest Jewish population in Poland, which swelled further to over 200,000 Jews as war refugees entered the city.Immediately after the Germans entered the city, Einsatzgruppen and civil collaborators organized a massive pogrom, which they claimed was in retaliation for the NKVD's earlier killings (though Jews were also killed during the NKVD purge).Many Holocaust scholars attribute much of the killing to the Ukrainian nationalists.