I read that the Chetniks were Serb nationalists and mostly targeted Croats - but during the course of World War II and the Axis invasion of Yugoslavia, after initially resisting, they began collaborating with the Axis and the Independent State of Croatia, which was an Axis puppet state.
What exactly motivated them to collaborate, if their main ideology was based on Serbian nationalism?
I'm sure someone will reply to you with a long post,but I will keep it short.So basicaly partisans-which were basically volunteers from all yugoslav nations(for example the city of Split were 70% partisan volunteers(even women volunteered) and even the ones that were stuck in the Ustase regime ran to volunteer there(my grandmother's brother ran from Zagreb to Hercegovina to volunteer)There were people from Serbia,Bosnia,Slovenia too,and tbh I don't know which nation was prevelant in the mix(probably none-that's why it worked so well. So back to the point,chetniks were scared by partisans who started moving forward after their retreat to the mountains of Hercegovina and started really claiming the land back. So basically the motivation was, the enemy of my enemy is my friend.