Wielkopolski, was sworn in Kalisz, before joining the ongoing Greater Poland uprising (1918–19) against Germany. The reconstruction continued and in 1925 a new city hall was opened. In the 1931 Polish census, Kalisz had a population of 15,300 Jews, nearly 30% of the city's total population. In 1939 the population of Kalisz was approximately 81,000. The Jewish population of Kalisz at the time was 27,000. World War II After the German invasion of Poland in September 1939, the proximity of the border once again proved disastrous. Kalisz was captured by the Wehrmacht after Polish resistance, and the city was annexed by Germany. In revenge for resistance, the Wehrmacht carried out massacres of Polish defenders, who were executed both in the city and in the nearby settlement of Winiary (today, a district of Kalisz). Over 1,000 people were arrested as hostages. Numerous Poles were arrested and murdered during the Intelligenzaktion aimed at annihilation of the Polish intelligentsia. Around 750 Poles from Kalisz, Ostrów Wielkopolski, and other nearby settlements were imprisoned in the Kalisz prison from September 1939 to March 1940, and most were murdered in large massacres in the Winiary forest. In November 1939, the Einsatzgruppe VI Nazi paramilitary killing squad murdered 41 Poles at the local Jewish cemetery; among the victims was pre-war Polish mayor of Kalisz, Ignacy Bujnicki. In April and May 1940, many Poles arrested in the region, especially teachers, were imprisoned in the local prison, and afterwards deported to the Mauthausen and Dachau concentration camps, where they were murdered. In Kalisz, the Germans established a Germanisation camp for Polish children taken away from their parents (Gaukinderheim). The children were given new German names and surnames, and were punished for any use of the Polish language, even with death (e.g., a 14-year-old boy was murdered). After their stay in the camp, the children were deported to Germany; only some returned to Poland after the war, while the fate of many remains unknown to this day. By the end of World War II approximately 30,000 local Jews had been murdered, and 20,000 local Catholics were either murdered or expelled to the more eastern part of German-occupied Poland (General Government) or to Germany as slave workers. In 1945 the population of the city was 43,000 – approximately half the pre-war figure. In 1945, Kalisz was restored to Poland, although with a Soviet-installed communist regime, which stayed in power until the