Off course it was not only Serbian territory.
The problem, from the very beginning is that Serbians were by far most numerous ethnicity inside Yugoslavia. In 1943. communists divided the majority of Serb population into 4 republics (and latter added 2 autonomous regions). There are stories that the whole idea behind that was to disunite Serb population, so that new state wouldn't be Serb dominated like Kingdom of Serbs, Croats and Slovenes was. Disregarding motives and if they are true, Serbs ended ethnically divided into many administrative zones. When the Warsaw pact and Soviet Union dissolved, the power balance between East and West (on which Yugoslavia relied) was gone. Some nationalities (Slovenes and Croats for start) started questioning their position, and new parties claimed that they would be better off outside Yugoslavia. On the other hand, Serbs would also be better off outside Yugoslavia, but they were in a stupid position, because if Republic of Serbia separated from Yugoslavia, there would still be a large part of Serbs left inside Yugoslavia. So, Serbia had no national interest to secede from Yugoslavia. That was the main reason why moderate Serbian politicians were favouring Yugoslavia.
Considering Bosnia, if you look at the war maps, you can see that in a small amount of time since the war broke out, the front lines were cemented and the didn't move much until the end of the war. These are the mapes from 1992:
https://upload.wikimedia.org/wikipedia/commons/9/9a/Map_of_war_in_Yugoslavia,_1992.png
And this is the ethnic structure of the region:
http://www.rastko.rs/istorija/srbi-balkan/img/fry4b.jpg
You see that they correlate very well with one another:
https://www.youtube.com/watch?v=YyoWem9Nvsc
So, if you think there was an aggressive war here, it wasn't. Nobody did conquer much of the "enemy" territory during the whole Yugoslav war. It was just a stalemate, going nowhere from the beginning. Croats and Bosniaks had no power to do it, and Serbs had no interest in Croat and Bosniak territory. Once only peasants (unlike Muslim craftsmen, merchants, officials, penman, etc) Serbs (who were ~40% of population) had in their legal possession <60% of Bosnian territory, while Muslims were mostly populating urban areas. That's why Serbs were pretty much satisfied with what they had even before the was started.
The whole Serbian idea was that Croats and Bosniaks can secede from Yugoslavia, but they cannot drag Serbians with them. If they want to secede they can do it democratically, and they can secede Croatian and Bosniak people, but they cannot secede administrative zones of Socialistic Republic of Croatia and Socialistic Republic of Bosnia and Herzegovina. On the other hand Croats and Bosniaks wanted to secede Croatia and Bosnia because that way they'd be getting more than they deserve. And that's how the war broke out. Western countries didn't do any good. They talked Bosnians 2 times into not accepting peace plans, as I've already posted somewhere.
First time in 1992. for Carrington-Cutiliero plan:
"
On 18 March 1992, all three sides signed the agreement; Alija Izetbegović for the Bosniaks, Radovan Karadžić for the Serbs and Mate Boban for the Croats.
On 28 March 1992, after a meeting with US ambassador to Yugoslavia Warren Zimmermann in Sarajevo, Izetbegović withdrew his signature and declared his opposition to any division of Bosnia."
https://en.wikipedia.org/wiki/Peace_...Cutileiro_plan
Second time in 1995, when Owen-Stoltenberg plan was in question:
https://www.youtube.com/watch?v=RUuh...youtu.be&t=25m
Badinter commission concluded they they recognize the borders of republics as state borders. That literally means that they gave advantage to some map lines that 7 communists have drawn in the middle of the winter of 1943. in some Bosnian hut, over democracy and will of the people. The decisions of that commission were illegitimate, illegal, contrary to Yugoslav constitution and international law.
They didn't want to cleanse it. If anything, the number of Albanians only rose during while Kosovo was under Serbian government. From ~500.000 in 1948. to ~1.600.000 in 1991.
https://en.wikipedia.org/wiki/Demographics_of_Kosovo#Ethnic_groups
Some claim that Serbians started ethnic cleansing during the NATO bombing. Serbians themselves claim, that Albanians fled from NATO bombing, for which they have some arguments in the fact that not a small number of Albanians looked for salvation in other parts of Yugoslavia controlled by Serbian army. Nevertheless, ethnic cleansing definitely started
after the NATO's war to stop ethnic cleansing.
This is the report of
OSCE observer who was on Kosovo:
"With the reversal of power, the 800,000 Kosovar refugees, created by the war, returned, supporting the KLA's policy of reverse intimidation and atrocities. This all but ethnically cleansed the majority of the 270,000 Kosovo Serbs and other minorities from the province."
http://www.iacenter.org/warcrime/rkeith.htm
This is what lord Carrington says:
"Nato bombing of Serbia caused, rather than prevented, ethnic cleansing in the Balkans, the organisation's former secretary general, Lord Carrington, said today.The bombing "made things very much worse" and the European Union had made "catastrophically stupid decisions" in its dealings with the former Yugoslavia, he added."
http://www.theguardian.com/world/1999/aug/27/balkans