Humans are not only unique in their abilities like problems solving and language, but also in their 100% dedication to the tribe.
I think it is this combination that allows for us to work together in such large groups and successfully.
Harari calls it "fictions" that bind us together, but that doesn't quite seem to work for me.
The question I ask is WHY do these "fictions" work so well?
Why would a Nebraska farmer go half way across the world and climb French beaches with German guns shooting at him?
Why are we so compelled to identify with a group?
A comedian has a great joke about this. Essentially, the WORST thing you can do to a person is put them in solitary confinement. Even being surrounded by criminals and prison guards is infinity better than being forced to be alone in a room. We desperately need to connect with people. It seems hard wired genetically to me.
I think culture helps serve this purpose of binding us together.
Art, music, theatre, and even sports are all a part of the process of group cohesion.
Group cohesion and dependency is so powerful that it's often the number one factor in determining which societies/countries/groups come out victorious with intergroup conflict.
A great book called "War and Peace and War" by Peter Turchin is a fantastic book to read if this concept interests you.
Another one, "Tribe" by Sebastion Junger also explores this topic.