Originally Posted by @Sweet Cleopatra
What is the origin of the grudge between neighbors?
Primarily the events of WWII. There are many documentaries I could upload for you if you are interested in any particular theater of war.
To give you an example, in 1992 local Serbs in Visegrad murdered hundreds of Bosnian Muslim civilians.
In this same town in 1942 about 6000 Serb civilians were murdered by Muslim and Croat fascists on the banks of the Drina River.
Another example, in 1992 on Mt. Majevica near Tuzla local Serbs killed about 60 Muslim civilians.
During WWII more than 500 Serbs were killed by Muslims at the same location.
That's just two examples, probably the ones that best illustrate the aspect of local revenge. There are many, many others.