Ironically, we do have a common enemy: The billionaires. Problem is the enemy has managed to brainwash almost half the populace into fighting for them.
Crazier idea. Let's create a fake racial group, and blame all our problems on them! We'll first manufacture a fake racial group that no real human could be mistaken for. Then we'll create fake history, fake documentation, maybe even invent an imaginary island they originate from. We'll run endless fake news stories showing them committing horrible crimes. Etc. Turn the hate machine up to 11.
It won't fool the most intelligent, but that's fine. Everyone who wants someone to hate will have someone to hate. And no one will have to suffer for it.
Bonus points, we can direct the idiots to start digging for them, then use the excavations to start building underground. It'll massively reduce the power need for AC due to global warming, and it would free up a ton of space for solar.
We have built within us a need to fight for survival. Natural selection has bred us to constantly be fighting for the top. When we get there we have no idea what to do with it.
We need something to fight against, that's why we all love under dog stories.
Uhm, no. I am fine with my belly full, a place to sleep and a confidence that within foreseeable future no big bad thing is looming over me or my family - with that settled, I have no need to fight.
It needs to be said that the above does not mean I am not going to out effort in things beyond that scope, but those efforts come from the desire to make the word a better place, not from some fighting
Bonus point: now look at how old humanity is. The Greek civilization, the Chinese, the Egypt... literally empires have come and gone, yet humans are just as dumb as thousands of years ago
We need something in common for people to get along. Enemies are just very easy things to share between groups, but common creeds, ideals, projects are all unifiers of equal power (though they're not nearly as convenient to find...)
Unfortunately I've found that unless they're given a very definitive common focus, humans are exceedingly prone to spending their free time carefully cataloging their differences.