When people can't get along, sometimes the effective solution is put up a barrier between the warring tribes.
Millions would not have died in genocide in Iraq, if Bush had followed Biden policy and divided the country into three fiefdoms at end of Iraq War. Shiites as their own tribe. Sunni as their own tribe. And Kurds as their own tribe. Put up big walls between the tribes, and the UN could police the borders.
Has worked for 50+ years, to date, on Korean Penisula.
I see the answer is that it is not people who (next comment to answer you)....I can't help asking myself as I read the arguments that seem to idealise people, with governments being all that is evil (you try being small and sickly as a child and just count how many will want to bully you), if they do not think walls and borders are needed, have they tried to prove their arguments and faith in the goodness of man, by removing gates and doors from their home - and if living in a house, do they also live without walls and electronic surveillance? Oh, sorry, they did say we would need to employ guards - so people who live close by are evil, but we can invite whoever we want from the most barbaric societies, because they will stay on their property. How does that work? They will never need to intrude by going into public spaces? Who is going to guard us in the public spaces? The barbarian guests? - or will we create a communal fund...uhm, should we differentiate and call those guards...what, police? Who collects the money to pay them? We appoint someone?
Are we on our way to ...closing a circle?
Yep. You've got it. I'll take a small amount of a necessary evil - government to enforce rule of law, as opposed to a mythical utopia with rule of man and rule of mob.
It is not people who cannot live together—it is governments. Borders only burden markets and hurt people.