Both of these were before nuclear weapons were a thing, though.

WWI didn't work very well.

See: WWII

From an american perspective where they stayed in the back during WW1 and had to be trained on the spot, and were perfectly happy to work with nazi germany in WW2 until shit hit the fan, sure.

For most of europe, it's a traumatic experience that led to dozens of millions of dead young adults, entire cities firebombed and razed to the ground, areas shelled so hard that even today their access is forbidden.

But I'm sure it's much easier from a position of a country that never had a single war on its territory.

That’s maybe a misunderstanding. I’m not advocating war per se. Yet I think it was right that the US didn’t stay on the sidelines.

I'm struggling to think of ways in which WWI 'worked out just fine' unless you count getting rid of the Romanovs and (most of) the Hapsburgs.

It helped to exaust alot of old colonial empires close to collapse, were the memberstates escaped to independence. Those two worldwars were what ate the british empire alive.

Good point. Yet not all of them if you consider Russia the last of the European colonial empires.

I certainly do not. (Look at France and Britain's overseas holdings)