Sports - A unifier?

Sports can be as much a unifier as it is a divider. It shows how much people like being in groups. I am supportive of a group for which I belong, but adverse to a group for which I don't. I find it interesting that the US tends to form rivalries within the US whereas the rest of world forms rivalries among countries. What does that say about us? Are we a little closed out by the world or do we keep the world out? You decide.