On 29 October 1918, the Croatian Sabor declared independence and joined the newly formed State of Slovenes, Croats and Serbs, which in turn entered into union with the Kingdom of Serbia on 4 December 1918 to form the Kingdom of Serbs, Croats, and Slovenes. The new kingdom abolished traditional subdivisions of Croatia, including Požega County, in 1922 when oblasts were introduced, succeeded by the banovinas of Yugoslavia. The Cvetković–Maček Agreement of 1939 created the autonomous Banovina of Croatia, incorporating the region. In April 1941, Yugoslavia was occupied by Germany and Italy. Following the invasion the region was incorporated into the Independent State of Croatia, a Nazi-backed puppet state as a zone under German occupation for the war's duration. Armed resistance soon developed in the country, and by 1942, controlled substantial territories, especially in Slavonia's mountains. After World War II, the region became a part of the Socialist Croatia within the Communist Yugoslavia.