Why did bosnia's mixed population cause a problem after bosnia declared independence?

Bosnia has three ethnic groups on their territory, Bosnians, Serbs, and Croats. Bosnians are mostly Muslim while Serbs are Orthodox Christians. When they declared their independence, Serbs didn't want that and wanted to remain a part of Yugoslavia while the Yugoslavian army tried to preserve the borders and didn't want to allow them to become independent. This led to a huge civil war with many bad things happening.