From Civil Politics:
One of the most general and robust findings in social psychology is the power of situations to shape behavior. For example, if you are in a situation where you are competing with others, you will tend to dislike them, whereas when you are cooperating with them, you will tend to like them. This is relatively intuitive, yet we often fail to appreciate this in practice, and then we end up amazed when arbitrary groups put in competition end up in deep conflict. If artificially created competitions can inflame divisions (e.g. sports fandom usually pits very similar people against each other), perhaps we can also manufacture cooperation to reduce division.