The Axis invasion of Yugoslavia saw Yugoslavia being overwhelmed and partitioned between the Axis nations of Germany, Italy and Hungary as King Peter II and his Cabinet fled into exile in London. Their exiled troops were the 1st Battalion, Royal Yugoslav Guards which saw action in North Africa and Italy in 1944 whilst attached to an Indian brigade. The Chetnik Detachments of the Yugoslav Army were established to carry out guerrilla warfare against the occupying forces, loyal to the royalist Yugoslav government-in-exile. Unfortunately, the Chetniks adopted a more Serb-oriented ideology which isolated them from potential supporters and led them to terrorize the Bosniaks, Croats, Muslims, etc. They would also collaborate with the Axis forces as they viewed Tito and his Partisans as the more dangerous threat. This is what caused the Yugoslav Partisans (National Liberation Front) to receive more support from all facets of Yugoslav territory as the Partisans grew in numbers and support. Your challenge is to establish a more successful Chetnik resistance movement that isn't Serb-oriented and remains loyal to the Yugoslav government-in-exile, ending up in control of most of Yugoslavia by the late 1940s. The Yugoslav monarchy must be retained - bonus points if the Chetniks and Partisans continue to work alongside one another.