One of the reasons for the break-up was the ethnic conflict: people felt that the other ethnicities in the country had better access to commodities, more wealth or were demanding too much. The conflict started with Kosovars demanding changes in their republic, and soon spread to other ethnicities demanding independence.
In more specific terms: Croatians and Slovenians wanted more autonomy, while Serbians wanted a more centralized government: and the war was a consequence of this difference in views.