Without a grand narrative to situation many “others” common traumas will produce narratives that produce enemy-others. You will tribe up against those enemy-others and humanity replays many bloody sad stories.
From the comments
2) Lack of binding ties. Like it or not, we live in a world of voluntary association. Community is inversely proportional to that. Humans historically lived in family-groups, small tribes, etc with essentially involuntary membership.
I don’t see a way to bring that back, but to make community stick people have to have enough commonality to act as a glue. Faith is a good start, but obviously not enough.
This is where I falter a bit. Going back to my college experience, the binder was a common set of experiences, similar age, shared interests, etc. I don’t know how to scale that.