The Serb and "Yugoslav" population/s within those entities did not want to break away. The Serbs were about 34% of Bosnia, more if you count ethnic Serbs who registered as "Yugoslavs." The Croatian Serbs 12.2% were/are definitely doomed in an independent Croatia (and Kosovo) as well. Much of the war was by local Serbs defending themselves and their villages with often no or little support by the Yugoslav army, which was disintegrating as the Croats, Muslims, Slovenes and Albanians defected into the separatist armies.
I know, Joan, that's part of why it was so messy. Unfortunately, the populations were in the pattern of a mosaic versus one coherent mass for each nationality.
The Croatian Serb population of 12.2+% before the war is only 4.5% according to Croatia's census back in 2001 or 2002. And Serbs say that the 4.5% is too high, and actually counts refugees who live in Serbia, but are registered for their pensions and the like in Croatia, yet DON'T live there. Many who can't even go back to their homes because they are destroyed or have Croats (some of these Croats from the diaspora - Australia or who have additional homes in Croatia) living in them to prevent Serbs reclaiming their former property.