People are unable to live in unity when there are ethnic and/or religious differences. It could be because one group is favored over the other for who they are and what they believe, maybe people are just intolerant and can't stand the differences (racism, discrimination, believing one is superior to the other), and/or one group had rights to a certain region in the beginning but were invaded or joined by foreigners taking up space, trying to integrate their own culture diminishing the native's culture, and using up their resources for self-benefit.