What guerilla warfare have they lost?

It's much harder to fight than it is to perform. Guerilla warfare generally succeeds by making the fight cost more for the foreign power than it's worth to them.

The polity waging guerilla warfare is usually defending their home, or their vision of it, and has nowhere else to go. As such, they have every incentive to hold out as long as possible. The foreign power is often only there for abstract interests, like economic concessions or 'anti-communism', and thus will not willingly endure the same level of losses as the polity waging guerilla war. They'll cut their losses after a certain amount of pain.

We're just on the other side of the equation in the 20th and 21st century - the foreign intervening power.

US COIN is actually very refined in theory, but requires cooperation and alignment of goals between the civilian US government, the US military, the occupied/liberated (depending on your point of view, or the war) civilian government, and the occupied/liberated military.

... it rarely comes together so smoothly.

It's about goals.

The whole point of guerrilla tactics is asymmetry. It's a smaller force with less resources maximizing impact.

In order to work against it, you have to go hard.

Going hard means wrecking support and resources. You know, like dumping agent orange, white phosphor, mustard gas, that kind of war crime level brutality.

If you do that, then if the goal isn't making enemies and spending large amounts of money, you're fucked. Because you'll spend billions and make enemies not only in the target region, but all around it, and for generations after.

Given enough budget and the freedom to destroy everything, guerilla tactics are easy to counter.

Even that isn't generally enough to subdue guerilla warfare. If it was, there would no longer be a 'Kurdish Problem'.

The actual way to work against it to offer a peace on acceptable (not necessarily favorable) terms to the partisans, that seems in good faith. Guerilla warfare rarely, if ever, peters out because of sustained military pressure. Military pressure can force them to the negotiating table, but if the occupying power has an insane position like "Kurds aren't real" or "We don't negotiate with terrorists", that won't help.

No offense, but I think the posts are more for answering OP's questions than piggybacking — especially when such facts can be found with a quick web search.

I'm sorry, but I don't know what you're talking about. I actually think that is a great answer, but the person I'm replying to is asking what guerilla war has the us lost. Like, a lot of them.

Cool, so instead of interacting on the post I'll go do research first gtfo

Ok... I interacted with your comment by giving my honest opinion. The down votes on my opinion suggests that people don't agree with me, so at least you've gotten that going for you.

The US has not learned a single core lesson from Korea, Vietnam, Afghanistan, and others.