Division of Yugoslavia after WW2

During war the little differences don't matter, the people on your side are your comrades and opposing people are enemies, but during peace the little differences form cracks in a unified state and sometimes cause it to collapse. During World War 2 the Serbians, Croatians, Bosnians and many others possessed a common enemy, the Nazis, which united them under one flag. After the war was won the cultural difference tore the country apart causing civil war. Countries with many different ethnicities are hard to sustain because humans are selfish. Unless they feel more connected to their country than their ethnicity they will try to improve the position of themselves creating mistrust. Another example of where this occurred was the Austrian-Hungarian empire. Luckily most people can overcome small differences because otherwise the sharing of ideas and goods could not occur and there would be constant warfare.