Human nature is constant pull between advancing self interest and attaining harmony within the group. We are gifted with individualism but that gift is a two edge sword. Conflict is the price we pay for our individualism. Only automatons would get along perfectly.
When we were small groups of hunter gatherers, those groups unable to sustain social harmony were destroyed. The movie Fast Runner illustrates this. ( Fast Runner ) When humans turned to agriculture and we collected into larger groups, societies tended to be regulated by rules and regulations often along religious lines. We tend to organize in an ascending hierarchy: individual, family, clan, tribe. Me against my brother but my brother and me against my cousin and me, my brother, and my cousin against the outsider. At the highest level this becomes nationalism. These alliances are natural and good. Some societies have put great stress on social order (e.g. the Japanese). The problem arises when those allegiances make it impossible to see the other as human.
There are people who have studied conflict resolution. One of the keys is to get both parties to see a benefit in a peaceful resolution. Peace occurs when the perceived benefit makes compromise possible.
Just as some individuals are sociopaths who are completely unable to put themselves into other person's shoes, so some societies get off track because of racism, religious zeal, or political indoctrination and set off to destroy all others.
We need to accept that differences exists and will not go away. We need to set up in widening circles mechanisms that help us mediate disputes. At the same time we need to realize that there are some who will never peaceful accept they are not the center of the universe and hence while conflict can be mitigated it will never disappear.
