I'm always open to be corrected, but as far as I know nations that formed Yugoslavia haven't actually fought each other meaningfully before WWI and even in that war Slovenians, Croats and Bosniaks were not involved independently, but as subjects of Austro Hungarian empire. There certainly wasn't the kind of animosity displayed as for centuries between France and England or France and Germany (as just two examples). It was really WW2 where one can observe the viciousness beyond fighting one's enemy.
I have my own views why things went south so badly and I agree with you that it was inevitable for YU to fall apart, but I find the often expressed argument that people living in our parts always did this very unpersuasive.