Traditionally, a shared cultural mythos- that is, the set of 'stories' that the society believes in and uses to bind themselves together- is one element of what holds societies together. Yes, even completely secular societies have their shared mythos and arguably even their own shared gods depending on how you look at it. Also, all human beings are naturally inclined to heavily favor anyone who is similar to themselves, especially regarding physical traits (shared blood).

We now have neither of these convenient pillars, so Professor Haidt suggests that we have to be highly cautious in the way that we structure our society, such that we can reap the creative benefits of diversity without leaning too far into the natural tendency of diversity to push people apart from each other.

I'm curious, what do you think holds a country together?