Civil war broke out in bosnia because the in bosnia wanted to be part of serbia but the rest of the population of bosnia wanted to remain part of bosnia.

The Serbs.  They wanted to have their own country.  This led them to launch an invasion that started the war.  Many were killed during this period.  The violence got to the point where even the U.N. was not able to stop it.  It took the intervention of the United States to finally end the conflict.

the answer to your question is:

strong-mayor system