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.

A death match between the presidents / prime ministers of the rival countries. The country of the winner of that match will win the war, and the country of the loser has to deal with the following consequences.

No hands for anyone. Possibly no feet too. Only the cooperative will survive.

Establish a global trade network in a way that everyone is completely dependent on everyone else.

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!

It's (theoretically) impossible -- you can't break someone's (ignorant and established) will/ideas/plans with words alone or treats. Most world leaders are megalomaniacs by heart, i.e they won't stop until they are done with what they want.

Universal basic income, universal food and shelter and education.

A single world spanning country.

If we don't kill ourselves off first it will probably happen eventually. Country sized used to be limited by things like communication latency, and the time it took to move forces around. Technology has shrunk the world so that those things no longer matter. The natural size limit on a country is almost certainly as large as the earth now.

It won't happen soon, cultures will take time to become similar enough to merge. Leadership structures take time to be absorbed into a greater one (EU style) or have to forcefully taken over (Chechnya style, thankfully very rare these days). But with no real impediment to countries growing larger, it will happen eventually. With no-one able to fund or support rebellion and modern technology making police actions extremely effective it may well last effectively forever.

Whether it's a democratic utopia, a dictatorial nightmare, or something in between for the common citizen is not yet defined. Either way, war, as in peer to peer conflict between sovereigns, will be over.

The only way to permanently end war is universal omnicide.

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!

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.

Economic democracy; if money and resources cause wars then why not let everyone have control? I will probably hear the human nature stuff but being social is just as if not more important than hurting your species/society.

An unfortunate combination of somehow achieving a post-scarcity, non-capitalist society with robust resource and population control.

But people are greedy and want "freedoms" that run counter to this.

Humans need to evolve to a state where love, compassion and being helpful to others is ingrained. At the moment we're just clever beasts.

Sadly though, I don't think we have enough time.

Put the ones in charge to the front line.

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

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

Easy enough, we just build a jail so big that we can fit the entire world inside of it, boom no more crime.

this is a bit grim but global-wide information control that shreds any information which will help the growth of the idea of overly patriotic but less enough to not kill the domestic culture (but i think, not necessarily always telling the truth). that will also promote the sense of global village and transnationalism. and relocate the idea of war to other rivalries like on sports or something, idk.

basically limit the free will without showing it. I can't think if it's gonna happen or this even possible.

Impossible. You can only deter and mitigate risk. But war is in our nature. War is uniquely human because it requires at least one civilization to wage.

The only way to stop war on Earth is to convince everyone here to go to war somewhere else.

So my plan is to militarize the school systems, manual military or scientific service at 18, create a federated republic under an international parliament, nationalize systems and get away from "profit" in exchange for progress, and go to war with the unknown to find "God" or whatever. Everyone who cant/wont can get UBI and healthcare and education a plenty, create art to their hearts content and do the "culture" thing.

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.

Put everyone in a time-out until they can play nicely with the other children (because let's face it, a lot of them are acting like children)

Kill every human, or all but one. As long as there’s at least two people, there will be conflict.