Well, they have been fighting themselves for thousands of years for a variety of reasons. In some ways you can argue they've never stopped the first war because they've never actually stopped fighting each other except when they have a common enemy.

With such a track record who's to believe they will ever stop fighting. I do know that for quite some time the small to large differences in the interpretation of the Quran is reason enough to kill each other.

My cousin married and Arab man from Quatar where they now live but often return to see family. He has explained so much about how Arabs hate and want death to other Arabs all due to slight disagreements on interpretations of the same religion.