group dynamics of hatred

Why does hatred last longer when it is between groups rather than individuals?

It is well-known that group dynamics can reinforce emotions. So that is one important factor... What is more interesting is that even when others try to soothe you with all the good intentions, they often end up prolonging the conflict. When they constantly take the steam off, there is never enough emotion built up to propel you to communicate with the subject of your hatred. Of course, when there is no dialogue, there can be no conflict resolution.