 Complete the following phrase:  The next stage of the anti-Semitic policy of the occupier was ghettoisation of the Jewish population, officially justified by economic, sanitary or political reasons. As an excuse to isolate Jews in closed districts, among other things, Germans used the Easter pogrom of March 1940, arranged from German inspiration by Polish extreme nationalists. The first Jewish ghetto was established in October 1939 in Piotrków Trybunalski. Over the next few months several more ghettos were created in the General Government and Warta Country, including the ghetto in Łódź February 1940. Beginning in September 1940, the ghettoisation process became more organized. In October of this same year, it was decided to establish a Jewish quarter in Warsaw. In March 1941 the ghettos in Kraków and Lublin were established. The process of ghettoisation in the Radom district of the General Government was rather at the latest in December 1941. After the outbreak of the 