There are a number of reasons. 1. They have been beset by enemies from the east and west and have always had to defend themselves. 2.Their culture and way of life has been tough in order to survive. Durig the medieval/early modern periods, in the Serbian controlled parts of what is now Croatia, the Serbian peoples were freedmen that lived in fighting communes - they provided the Hungarian and Austrian armis with the bakone of their armies. In return for being soldiers and fighting in causes not of their own they were given special tax and legal rights. 3. They have an independent culture and have refused to bend to any super powers will. In 1914 it was Austria-Hungry, in 1940 it was Hitler and more recently the Americans. They do this despite never being able to win. 4. They are a very insular people and are percieved to be arrogant, much like the Jews. In many ways they are very arrogant. Their neighbouring peoples see this unwillingness to mix and resentment surfaces. Many parallels exist with the Jewish suffering in WWII. Sebias neighbours, with German aid, murdered over 10% of the Serbian population. This treatment of them , in turn makes them feel aggrieved an so the cycle of violence continues. An interesting people that have been demonised by Western Propaganda