Let’s first address all the “nature” and “biological” not-really-true claims.

The Batek people of Malaysia are so averse of killing other humans that refuse to do it even when threatened with slavery https://peacefulsocieties.uncg.edu/societies/batek/

So, war is cultural, not biological.

Second, why do we do war?

At first glance, is for scarce resources, for survival.

But look at the modern wars. Are they for survival? Are they for resources that we need to survive?
No they are not.
They are for power.

But whose power?
The power of those who actually have to fight and die?
Certainly not.

The power of the rulers, who are greedy for more power.

Most people need to be scared into going to war, need to be convinced that they are defending their families and their “people”.

This is why rulers work very hard to build national identities, the good “us” vs the evil “them”.

Here we need three things:

1. We need a culture that knows how to recognize those greedy for power, those with a desire to dominate, and see them as the threat to freedom that they are, ie some sort of https://en.wikipedia.org/wiki/Leveling_mechanism
   There are several cultures that do that, but it has to be a deliberate and conscious thing.

2. We need to rethink our identities, national and not, because those identities are used to define the “other” that is ok to harm and kill.
   A way to do this is to make sure that people who want to travel and visit other groups can do so easily: this will help the various groups understand and humanize each other.

3. We need a culture that stresses the importance of non-violent conflict resolution.
   Because if all you know is violence, then that’s what you will use.

I mean, easier said than done of course, but I think that knowing the direction makes it easier to reach it.

For further reading on the subject, I would recommend Bob Altemeyer’s “The Authoritarians” and Graeber & Wengrow’s “The Dawn of Everything” from the top of my head.

Universal basic income, universal food and shelter and education.

That’s another rule. No wishes containing the word ‘all’. Guaranteed ironic consequences.

I don’t think anyone’s going to miss wars.

Star Wars, Thumb wars, wow, Storage Wars!

set aside a space for any country that wants to war, they have to deploy troops/etc there & fight there. anything goes, any atrocity or tech someone wants to use. but everyone is always watching - cameras and sensors everywhere and 24x7x365 coverage on a freely accessible dedicated stream/tv channel paid for by taxes levied against the populace of any country that chooses to war in that space.

it’d be the most highly watched stream ever, forever.

Did you watch Shiny Happy People? Apparently Christian fundamentalists believe the world population can fit into Jacksonville, FL. There’s the answer. Anyone who wants to start a war has to go live in Jacksonville. Build that wall!

Put the ones in charge to the front line.

There is no solution to that. It is a cold, hard reality of living on a planet with limited resources. We all might hate war (and for good reason, obviously), but it isn’t like animals don’t fight for territory either. Just happens that humans found a way to make it a few orders of magnitude more extreme.

Make the old men fight each other and soilder just refusing to follow orders that seem stupid

Equal distribution of wealth and power, along with trying to create universal standards of communication (I.E. speaking reading and writing) would help probably.

Plus universal access to education and birth control. And ENFORCING equality by making sure there is no such thing as inherited wealth. Each new generation would have to start form the same point. I know it might seem a little extreme, but I think it’s the only way to prevent oligarchies, monarchies, and huge concentrations of power that distort society from forming.

Plus, guaranteed clean food, water, housing, and basic healthcare for all. Get rid of the reasons for conflict, and make sure those who want to start conflicts can’t ever mass enough power to start wars and we won’t have them. A lot harder to justify fighting when you personally have to do it all yourself because you can’t order others to just do it for you.

It would take way more but the first step it would be to remove religions. And not only because most are not peaceful in principle but also because some religions see others as a target. Even small difference in beliefs could spark a vicious and long standing conflic, like Catholics Vs protestants.

Like others said, struggle is in human nature. But it is possible to shift it to other domains: art, science, exploration. To prevent this stuggle spill back into physical violence, there should be broad consensus on basic rules, effectively enforced.

So I’d say, build this consensus, which will probably need to rely on abundant renewable enengy, some form of UBI, equality, and stronger international institutions, but will not spotaneously evolve towards unsupportable preferences of some groups.

Put everyone in a Matrix and let the A.I. lead the humanity

The question is ill-posed.

War is just a tool, a collective act of violence that a group of people do against another in order to obtain a result. It’s always sad and it’s always bring sufference, but one could say sometimes it’s necessary. If you cancel war from the world witouth changin anything else, you will ends up probably damagin more the one with actually less power, since violence is usually the last resort in order to confront someone that hold political, economical and soft power upon you.

If you wanted to ask how we go to a situation when wars are not necessary and they are actually the less convenient and effective way to obtain collective or personal results, so that we ends up with no actual war are started, here’s my answer. We need to build a system that minimize close to zero the difference in power (every kind of power) between people, and we need to build an efficient an relieble system to intermediate and resolve the inevitable conflict between people and groups.

Kill everyone. No people, no wars! Win/win in my book

The only way to end all wars is for all people to fully control the instinct of domination with rational mind. It’s all about education and self-awareness. Making people rational creatures