They turned soccer stadiums into battlegrounds and then fought real wars.
Now, nearly 20 years after the wars ended, the Balkan nations are mulling the formation of a joint soccer league, hoping to give a new life to the once-thriving competition.
European soccer's governing body is considering a league that would comprise the former Yugoslav states — Serbia, Croatia, Bosnia, Montenegro, Slovenia and Macedonia — plus maybe Bulgaria and Hungary.
The idea, which has triggered controversy in the region, is to try to improve the quality of club soccer in the Balkans, which has deteriorated since the bloody breakup of the former Yugoslavia in 1991.
The main concern is security in the stadiums with ethnic tensions still ripe, with the Union of European Football Associations accusing Serbian and Croatian hooligans of being among the most notorious in Europe for violence and racial outbursts.