The Warsaw Ghetto Uprising was an uprising by the Jewish resistance in the Warsaw Ghetto in German-occupied Poland during World War II to oppose Nazi Germany's final effort to transport the remaining ghetto population to the gas chambers of the Majdanek and Treblinka extermination camps in 1943. It was the largest single revolt by Jews against the Nazis during World War II. After the Grossaktion Warsaw of summer 1942, in which more than a quarter of a million Jews were deported from the ghetto to Treblinka and murdered, the remaining Jews began to build bunkers and smuggle weapons and explosives into the ghetto. The left-wing Jewish Combat Organization (ŻOB) and right-wing Jewish Military Union (ŻZW) formed and began to train.