Bosnians are Bosnian Serbs (Orthodox Christians), Bosnian Croats (Catholic Christians) and Bosniaks (Muslim).

As Yugoslavia was slowly balkanizing :), there was a referendum in Bosnia as well, where it was voted primarily by Croats and Bosniaks to leave former federation. It was opposed by Serbs who wanted to stay alongside their own countryman inside Yugoslavia. Complicated long story short, war was fought primarily between Serbs on one side and Croats and Bosniaks on other, though there are instances where Croats fought Bosniaks while Serbs were watching on the side. Even though there was common enemy in Serbs two other parties were pushing their own agendas, getting into conflicts frequently.

This comes from situation where Bosniaks lived in cities and Serbs in rural places, while Croats lived in two separate regions of Bosnia and Herzegovina, one along Neretva and other along Sava river where both Serbs and Bosniaks are present to greater or lesser extent.

Today there are two entities Serb Republic, majority Serbs, and Federation of Bosnia and Herzegovina, majority Bosniaks, though Croats are pushing in some way for creation of Croat majority entity of Herzeg Bosnia, situated around Neretva river.

Outside Bosnia and Herzegovina, Bosniaks didn’t fought in Yugoslav wars, at least not in some significant part, it was Serbs against everyone else. There are instances of guerilla soldiers from Italy fighting on Albanian side in Kosovo in 1999.

This is pretty shortened version of abnormaly fucked up situation, and I wouldn’t wan’t to go into details.. hope it somewhat clarifies your question...