If Yugoslavia didn't break up, and Serbia, Montenegro, Croatia, Bosnia, Slovenia, and Macedonia could collectively field a single team... they could have won the World Cup in 1994 and the European Championships in 1996. Look at the players that were around in the early to mid 90's for these countries...
Zvonimir Boban
Robert Prosinecki
Davor Suker
Robert Jarni
Dejan Savicevic
Predrag Mijatovic
Dragan Stojkovic
Sinisa Mihajlovic
Alen Boksic
And a few more I can't think of right now. Could've been a great team.