They turned football stadiums into battlegrounds and then fought real wars.
Now, nearly 20 years after the wars ended, the Balkan states are mulling the formation of a joint football league, hoping to give a new life to the once-thriving competition.
UEFA is considering the 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 a lot of controversy in the region, is to try to improve the quality of club football in the Balkans, which has dramatically deteriorated in independent leagues since the bloody breakup of the former Yugoslavia in 1991.
The main concern is security in the stadiums with ethnic tensions still ripe and with UEFA accusing Serbian and Croatian hooligans of being among the most notorious in Europe for violence and racial outbursts.
After all, the Yugoslav wars were initiated on the football pitch 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 other in real battles.
One proposal tabled at a recent meeting between local and UEFA officials is that visiting fans would initially be banned from traveling to the 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 that football, 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 - the first encounter as independent states between the bitter Balkan rivals.
Fearing clashes, the Croatian and Serbian football associations imposed a travel ban on Serbian fans. The ban will remain in place for Croatian fans when the two national teams meet in the return leg in Serbia later this year.
UEFA - which has twice in two years warned both countries that in case of continued fan trouble, their teams could be banned from international competitions - said it will keep a close watch on the Friday match at Maksimir, the same stadium where the 1990 fan rioting took place.
Many think that the idea of a regional league - reportedly to be launched as early as 2015 - is highly premature, mainly for security reasons.
''For now, the most important thing is to eliminate violence from the stadiums in the Balkans,'' Serbian FA president Tomislav Karadzic said. ''Only then we could start thinking of a regional league.''
Vahid Halilhodzic, a former Bosnia international and ex-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 radically boost the quality of football in the region.
''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.
''The decision has to be made high up, by politicians. They say they want reconciliation, so here is their chance.''
Those who support the joint league say it would prevent stars such as Croatia's Luka Modric of Real Madrid, Serbia's Nemanja Vidic of Manchester United or Bosnia's Edin Dzeko of Manchester City from permanently leaving their countries and joining rich foreign clubs.
The former Yugoslavia league produced such clubs as Red Star, which was European champion in 1991. But since the start of the Champions League in 1992, the former Serbian powerhouse has failed to qualify for the last 32 in the competition.
Even when they make it to the elite European competition - which has happened only seven times in the Champions League's 20-year history - the former Yugoslav teams suffer with poor results. Dinamo Zagreb, now the most successful club in the region, was responsible for the region's last win at that level, beating Sturm Graz 3-0 back in 1999.
UEFA President Michael Platini in 2009 said he was neither for nor against the regional league concept. With his efforts to dilute the hegemony of west European clubs in the Champions League, he is apparently prepared to green light a Balkan league.
If UEFA negotiates the joint league, it would lead to direct Champions League and Europa League berths for its most successful sides. That proposal, however, could be another stumbling block, 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 striker who has become the 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 the joint Balkan competition because of their hatred for the 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.
