During the German invasion of Poland, which started World War II, the town was captured by Germany on September 2, 1939. During the subsequent German occupation the local Polish population was subjected to various crimes, including massacres, expulsions, deportations to forced labour and to Nazi concentration camps. Already in September 1939, the Germans destroyed the pre-war monument to the Greater Poland Uprising participants. Around 4,000 Polish civilians taken from Gniewkowo and the nearby cities of Inowrocław, Bydgoszcz and Toruń were executed by the Nazi Germans in the woods surrounding the town. Among the victims were Polish teachers, principals, farmers, musicians, railwaymen, local officials (see "Intelligenzaktion"). Inhabitants of Gniewkowo were also among 56 Poles massacred in a prison in Inowrocław on October 22–23, 1939. In 1944–1945, the Germans also operated a female subcamp of the Stutthof concentration camp in the town. Polish and Soviet troops took Gniewkowo on January 21, 1945. The town was restored to Poland, although with a Soviet-installed communist regime, and thus begun the 44 years of Communist Poland.