Yugoslavia only existed from the 1940s to the 1990s because

of nationalism and wars

Explanation:

Yugoslavia was formed in the 1940's, with its leader being Tito. This South Slavic country emerged with the merging of Serbia, Croatia, Bosnia, Macedonia, Slovenia, and Montenegro into one state. Yugoslavia was a socialist country, and even though it had most of the traits as the other socialist countries, it seems to have been much less extreme, and the people in general had it relatively good. The country was developing well and it was prospering, becoming a force to be reckoned with, but also remaining neutral during the Cold War period. This lasted until the death of Tito. Once Tito was gone, everything quickly started to fall apart. The extreme nationalism emerged as the dominant force in the two biggest states, Serbia and Croatia, and the tensions soon led to military conflict. One by one all states started to declare independence, with Macedonia being the only one that didn't engaged in war with anyone in the early 1990's.