Restructure society to value cooperatation over competition.

Break down unjustifiable hierarchies where possible and reasonable. The flatter the power structure is without sacrificing much in the way of efficiency, the better.

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

Mass extinction event. Breed out aggression from our species we seem to be doing that but slowly. Space mining could potentially stop us from having war in Earth at least. AI takeover have everyone live on their own virtual reality paradise. For the most reasonable I think the best way to end wars is education and uplifting poverty nations not exploit them.

Edit: Or we can just be like Switzerland be a direct democracy, with how slow they decide things it will be highly unlikely to go to war at all.

When there’s no war, people like Hitler won’t have any opposition to their rise to power. Haiti never gains independence. We’d never have escaped feudalism.

Most wars are stupid bullshit and suck ass. The military, especially the US military, is the biggest waste of money ever. That doesn’t mean that war isn’t directly tied to lots of positive things like innovation. There’s so much medical, industrial, and geographical knowledge we wouldn’t have if it wasn’t for some war, and that’s just the tip of the iceberg. People’s ideas will always conflict because different groups of people are going to have goals unique to them that clash with others

Now if you were to ask how to stop unnecessary wars, better more efficient rulers. Most of the people in power today are complete hacks. It’s crazy

But I don’t think we’ll ever get rid of war and I don’t know if that’s necessarily that crazy? Ultimately it’s apart of how we grow as societies

The complete extinction of the human race

Nuclear deterrent. If that fails, nuclear annihilation. Either way, there will be no more wars.

Rename to “armed conflict” or “special military operations”

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.

Make those who declare war to actually fight the war. Put the two countries president on each side of an arena with some swords to fight to death, the one who lives wins the war. I’d record and pay pee view or something and the money raised would pay for homes for the poor in each country

Kill all humans

Kill every human being. No people no war.

Since you stipulated our species, to me, the answer is an external threat to the whole. Aliens, higher or lower dimensional creatures, cryptids, flame unicorns sharting lava, even angels or demons if we want to get real wild.

Even just the threat of an existential terror such as these and probably a lot I missed, (feel free to add to the list! Feed me your existential threats!) has the potential to bring the species together to fight on a larger scale.

However this doesn’t eliminate war just moves the focus. So I’m not sure if I’ve answered your question or not but I had fun doing it!

Benevolent global AI dictator. These never go wrong in sci-fi after all.

(has to be true AI like Daneel Olivaw, not this fake LLM crap though)

There is this dystopia anime series called From the New World. The premise is a portion of humanity gained psychic power and led to the collapse of society because it’s so powerful that order could not be enforced. Far into the future there’s a cluster of communities that’s able to exist, and the way they went about it was to genetically engineered humans so when they harm another human it triggers body functions that make it harder for them to breath and other things. Killing another human also kills the aggressor. It kind of works on the interpretative level so it’s possible that using drones could still have an effect, probably.

Even in the story they explored ways to circumvent it though, but that’s kind of a tangent.

Democracies rarely go to war with each other. Add mutual economical dependency to that and you have a strong base to avoid armed conflict. The EU is a good example for that.