Recently I suddenly realized how different traditions Europe and the US have when it comes to dealing with separatism.
The US has a tradition of suppressing rebellions. Its civil war was the most striking of these but in the first decades when the US was independent there were quite a few smaller rebellions.
Europe's experience is quite different. In the last centuries it has developed more and more towards nation-states. The experience is that when people don't want to live together they sooner or later will find a way to achieve that. Sometimes war played a role, like when the Habsburg empire fell apart after World War I and the many smaller border changes along ethnic lines after World War II. Nowadays nobody is worried about the fact that there is a real chance that in the coming decades Northern Ireland and Scotland may choose to leave the UK. Neither is there much worry about the fact that Belgium may fall apart.
Europe has little choice in this. While in the US after a rebellion was suppressed the people involved reentered the great melting pot in Europe your nationality tends to stay with you. If you are on the losing side of an ethnic conflict you may be subjected to discrimination or even ethnic cleansing. It is not totally impossible to create a melting pot in Europe: Turkey is a recent example. But it requires major commitment. And the melting pot is seldom universal: the US had its Indians and its Blacks and Turkey its Kurds and Greek who were not invited. Commitment to a common identity is rare and efforts to impose it from the outside - as we see in Bosnia - are doomed to fail.
It should be noted that the US is not above fueling ethnic tensions among its adversaries. An important reason that the Habsburg empire fell apart was that the US had been fueling nationalism under its minorities as part of its World War I strategy. The US also liked to fuel ethnic tensions in the USSR and has more recently been accused of fueling ethnic tensions in Iran and China.
Regarding Yugoslavia at first the European method of indulgence towards separatism dominated. It led even to ignoring of the Yugoslav constitution and insufficient attention to negotiations. Interestingly later on the US got involved and it put great value on the territorial integrity of Croatia, Bosnia and Kosovo. This was according to their tradition.
I think that this mix of traditions has led to a worse result than when either of the traditions had been used consistently.