"Harmony" enforced by an iron hand. I'll answer your question with a question - if they were in such harmony, why did it break down?
The 1990’s war was not caused by the citizens of Bosnia. It was caused by the desire of Milosevic and Tudjman to divide Bosnia and annex its portions to Serbia and Croatia respectively.
This was somewhat similar to the scenario forced upon Poland at the beginning of WW2 when Germany and USSR invaded and divided the country.
First attrocities in Bosnia were committed by paramilitary forces imported from Serbia. The only reason why Serbs did not overrun Bosnia completely in 1992 was the fact that they did not have enough motivated foot soldiers in their military and the NATO enforced the no-fly zone, erasing this advantage of Serbs who had taken over weapons from the former federal army.
Was it a natural harmony or iron fist of USA that transformed western Europe after WW2? How did the nazi Germany become a democracy? How many USA soldiers are still present on German soil?