title: Jewish ghettos in Europe
context: Nearly complete genocidal destruction of the Polish Jewish community took place during the German and Soviet occupation of Poland and the ensuing Holocaust. The World War II ghetto-system had been imposed by Nazi Germany roughly between October 1939 and July 1942 in order to confine Poland's Jewish population of 3.5 million for the purpose of persecution, terror, and exploitation.[28] The Warsaw Ghetto was the largest ghetto in all of Nazi occupied Europe, with over 400,000 Jews crammed into an area of 1.3 square miles (3.4km2), or 7.2 persons per room.[29]  The Łódź Ghetto (set up in the city of Łódź, renamed Litzmannstadt, in the territories of Poland annexed by Nazi Germany) was the second largest, holding about 160,000 inmates.[30] Over three million Polish Jews perished in World War II, resulting in the destruction of an entire civilization.[31][32]
question: When were ghettos first established?
answers: roughly between October 1939 and July 1942