The 13th Waffen Mountain Division of the SS Handschar (1st Croatian) was a mountain infantry division of the Waffen-SS, an armed branch of the German Nazi Party that served alongside but was never formally part of the Wehrmacht during World War II. At the post-war Nuremberg trials, the Waffen-SS was declared to be a criminal organisation due to its major involvement in war crimes and crimes against humanity. From March to December 1944, the division fought a counter-insurgency campaign against communist-led Yugoslav Partisan resistance forces in the Independent State of Croatia, a fascist puppet state of Germany that encompassed almost all of modern-day Croatia, all of modern-day Bosnia and Herzegovina, and parts of Serbia.