Why have there been large coalitions of countries throughout history that come together to draft agreements about the boundaries of war and what constitutes a war crime (like the Geneva Convention), b

"I'm going to start a war."

"Stop, That's illegal!"

"Who's going to stop me? You and what army?"

"This army!"

And then they fight a war.

A lot of people on here are making the point that war is profitable in many cases. They aren't wrong, but it's much simpler than that and has nothing to do with money. The entirety of the sovereign state based system we live in is predicated on the premise that to consolidate power you have to have a monopoly on use of force. And when you have a bunch of individual states claiming sovereignty over a bunch of individual territories, the only way that sovereignty is actually worth anything is if that state is willing to put up a right to prove it. I think the only way we will ever get away from war in the way we see it now is by moving onto an Earth-encompassing single state. We are a long, long way off from that.

The U.N. doesn't have the authority to make a unilateral decision like that to begin with.

And, since they only way to enforce such a rule would be by using armed forces to stop an illegal war, you see why it's a pointless rule.

Besides, as horrible as war is, it serves a purpose. Even "illegal" wars like invasions of sovereign nations or pogroms serve a purpose, we just don't like those purposes usually. They still serve as a form of resolution to tensions between warring parties. Sometimes, one of those parties is aggrieved and war is the only way to prevent whatever is happening from continuing.

You can't just ban war, war is the state of existence when all other forms of conflict resolution between populations have failed. That will never, ever go away unless humanity ceases to be diverse and complicated. As long as there are multiple cultures, nations, and peoples, there will be conflict of some kind.

What face war has may differ. We might get to a point where war is always warm or cold rather than hot. But it's just as likely that we could end up in a state of constant warfare where a majority is steadily rejected, with violence, by the minority that objects to the differences between each other, no matter what those differences are.

Let's use a pretty current possibility. Let's say Thad the march to fascism here in the US succeeds. A president, Congress, and Supreme Court all dominated by the hate filled groups takes control and enacts laws that prevent their removal through other means.

Should we not rise up? Should we just shrug and say "oh well, they win, we can't have war."?

No. You fucking beg, borrow, or steal weaponry and you take the nazis/fascists down, just like the world has had to keep doing for most of a century. Yeah, you'll be fighting in an asymmetrical war, but that's still better than rolling over.

I mean, if would be better to rise up before things get to the point where there's the capability to dominate current structures, but that ain't gonna happen.

You can't wave the wand of law and banish war. The only way to banish war is shifting to a single, unified consciousness. That's impossible.

As mentioned, war is a billion dollar industry. But also, international law is complicated to enforce. Countries aren't so easy to control that you can just fine them unless there is a greater consequence for not doing so. That greater consequence is often war, or some form of sanction.

But you also have nuclear powers in the mix, making war an ineffective method of enforcement, because the risks of war between two nuclear powers is greater than can justify whatever enforcement caused it. Leaving the next best tool to be sanctions. But not every country will honor those sanctions, and you create these crazy little countries like Iran or North Korea, who build nuclear weapons and cozy up to your enemies instead of you.

Unfortunately, war is a billion dollar industry...

It makes no difference what men think of war, said the judge. War endures. As well ask men what they think of stone. War was always here. Before man was, war waited for him. The ultimate trade awaiting its ultimate practitioner. That is the way it was and will be. That way and not some other way.

Note: I'm not an expert on the topic of the UN or geopolitics

Two countries declare war on eachother and the UN goes:

—"Stop! That's against the law!"

Then the UN proceeds to attack the countries to stop the war, starting another war.

It's meant to be a like minded agreement where if it ever came down to the countries going to war with each other, then the agreement is how war would be conducted. Take the Geneva Convention for example. If the US went to war with England for some reason, then the Geneva convention would be their ultimate code of conduct for the war to avoid unnecessary casualties, the management of pows and adequate reasons for ceasefires. It's more just guidelines as they are rules. However if you're a country outside of those agreements, then the guidelines don't apply. It seems arbitrary, but the concept comes from a good place imo

They can as long as the country is not a nuclear power. Because nuclear weapons are the only real prevention.