The establishment of the Kingdom of Yugoslavia in 1929, however, brought the redrawing of administrative regions into banates that purposely avoided all historical and ethnic lines, removing any trace of a Bosnian entity. Serbo-Croat tensions over the structuring of the Yugoslav state continued, with the concept of a separate Bosnian division receiving little or no consideration. The famous Cvetković-Maček agreement that created the Croatian banate in 1939 encouraged what was essentially a partition of Bosnia between Croatia and Serbia. However, outside political circumstances forced Yugoslav politicians to shift their attention to the rising threat posed by Adolf Hitler's Nazi Germany. Following a period that saw attempts at appeasement, the signing of the Tripartite Treaty, and a coup d'état, Yugoslavia was finally invaded by Germany on 6 April 1941.
World War II (1941–1945)
Nazi forces in World War II, all of Bosnia was ceded to the Independent State of Croatia (NDH). The NDH rule over Bosnia led to widespread persecution and genocide. The Jewish population was nearly exterminated. Hundreds of thousands of Serbs died either in Ustaše concentration camps or in widespread mass killings by Ustaše militia. Many Serbs in the area took up arms and joined the Chetniks; a Serb nationalist and royalist movement that collaborated with the Axis occupiers and, on occasion, with NDH forces. Some Chetniks committed atrocities against Bosnian Muslim and Bosnian Croat civilians in regions under their control. Consequently, several Bosnian Muslim paramilitary units joined the NDH forces to counter their own persecution in the hands of the Serbs in Bosnia. On 12 October 1941 a group of 108 notable Muslim citizens of Sarajevo signed the Resolution of Sarajevo Muslims by which they condemned the persecution of Serbs organized by Ustaše, made distinction between Muslims who participated in such persecutions and the wider Muslim population, presented informations about the persecutions of Muslims by Serbs and requested security for all citizens of the country, regardless of their identity. According to the US Holocaust Museum, 320,000-340,000 ethnic Serbs were murdered. According to the Yad Vashem Holocaust Museum and Research Center, "More than 500,000 Serbs were murdered in horribly sadistic ways, 250,000 were expelled, and another 200,000 were forced to convert" during WWII in the Independent State of Croatia (modern day Croatia and Bosnia).Bosnia was the geographical mother of the partisan movement, providing ample space amongst its mountains for training and development.
Starting in 1941, Yugoslav communists under the leadership of Josip Broz Tito organized their own multi-ethnic resistance group, the Partisans, who fought against Axis, Ustaše, and Chetnik forces. They too, committed numerous atrocities, mainly against political opponents of all ethnicities. Some Bosnian Muslims joined the SS Handschar division, an SS division of the Nazis that pledged allegiance to both Adolf Hitler and NDH leader, Ante Pavelić. The division was the first SS division which was constituted of non-Germans. On 25 November 1943 the Anti-Fascist Council of National Liberation of Yugoslavia with Tito at its helm held a founding conference in Jajce where Bosnia and Herzegovina was reestablished as a republic within the Yugoslavian federation in its Ottoman borders. Military success eventually prompted the Allies to support the Partisans. On 6 April 1945 Sarajevo was captured by the Partisans. The end of the war resulted in the establishment of the Federal People's Republic of Yugoslavia, with the constitution of 1946 officially making Bosnia and Herzegovina one of six constituent republics in the new state.