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.
The Yugoslav wars were initiated on the soccer field when Dinamo Zagreb and Red Star Belgrade fans clashed in the Croatian capital during a league match in 1990, and later joined paramilitary forces to fight each.
One proposal made during a recent meeting between local and UEFA officials is that visiting fans initially would be banned from traveling to regional league matches. The formula has worked in a joint basketball league that has been played for years without major fan troubles.
But many fear soccer, the most popular sport in the region, is altogether different - a matter of national pride, the sense that has often resulted in violence in the Balkans.
A major test of whether such national emotions could be put under control is a World Cup qualifier between Croatia and Serbia on Friday in Zagreb - their first meeting as independent states.
Fearing clashes, the Croatian and Serbian soccer federations imposed a travel ban on Serbian fans. The ban will remain in place for Croatian fans when the two national teams meet in another qualifier in Serbia in September.
UEFA has twice in two years warned both countries that in case of continued fan trouble, their teams could be banned from international competitions. UEFA said it will keep a close watch on the Friday match at Maksimir Stadium, where the 1990 fan rioting took place.
Many think that the idea of a regional league - which could be launched as early as 2015 - is highly premature, mainly for security reasons. The Balkans also have been one of the areas where there have been accusations of match-fixing,
''For now, the most important thing is to eliminate violence from the stadiums in the Balkans,'' Serbian Football Association President Tomislav Karadzic said. ''Only then we could start thinking of a regional league.''
Vahid Halilhodzic, a former Bosnian national team player and a former coach of Dinamo Zagreb, agreed.
''It would only be an opportunity for right-wing extremists to express their frustrations,'' he said. ''Wartime emotions are still high, and football should stay out of it.''
Others say such a unified competition would bring fans back to the now near-empty stadiums, attract foreign sponsors and boost the quality of soccer.
''The joint Balkans league would lead to a higher quality of football, it would attract more interest with football fans and the financial gains for clubs would be bigger,'' Dragan Dzajic, former Yugoslavia star winger and now Red Star Belgrade director, said. ''That being said, I don't think that it will happen in the near future. The prospect of fan violence is often used as an excuse for the people who are opposed to the idea of a joint competition. I myself am not sure as to which way it would go, but I can see that others do it with no problems. Take basketball, for example, it attracts huge crowds and is played indoors, that makes it even harder to organize when it comes to security.
Those who support the joint league say it would prevent the departure of stars to high-revenue clubs, such as Croatia's Luka Modric (Real Madrid), Serbia's Nemanja Vidic (Manchester United) and Bosnia's Edin Dzeko (Manchester City).
While the former Yugoslavia league produced powerhouses such as Red Star, which was European champion in 1991, the separate leagues have struggled. Dinamo Zagreb, now the most successful club in the region, was responsible for the region's last Champions League win, 3-0 over Sturm Graz in 1999.
UEFA President Michael Platini in 2009 said he was neither for nor against the regional league concept. If UEFA approves a joint league, it could lead to direct Champions League and Europa League berths for its most successful clubs. That could become an obstacle, because each Balkan country seeks to have its own clubs in the major competitions.
''We cannot go back,'' said Davor Suker, the former Real Madrid forward who is president of Croatia's FA. ''We all have our countries and we all want to be winners and have our teams play in Europe.''
Red Star fans, who vehemently oppose a joint Balkan competition because of their hatred for Croats, recently displayed a huge flag with a crossed out map of the former Yugoslavia, reading: ''No to the Regional League.''
Dinamo Zagreb fans - the Bad Blue Boys - share the hatred, this time for the Serbs, and have a warning: ''If someone wants another war, let's have the league!'' said Damir Kusic, a Dinamo fan.
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Marko Drobnjakovic in Serbia and Darko Bandic in Croatia contributed to this report.
