Framing everything in relation to WW2 actually holds people back from looking at the problem and formulating an actual solution. Almost every relevant parameter is wildly different: analogies based on simplified similarities are seductive but fundamentally flawed.

It seems like we want to make it happen again just because it's the story we know.

But it's not going to happen again. There might be a bloody conflict, but it will not have meaningful similarities to WW2.

Climate change is the other big one, but given two different sources of great future suffering and dystopia, the one that's rooted in premeditated evil in the heart of man is much more distressing to me than the one that's rooted in stupidity and negligence (not that there are no evil parties benefiting from climate change, but malice upsets me more than greed).

But those are just my personal feelings; there's no ranking tragedies, really, and I feel equally powerless against all of them anyway. So take your pick on which one you're going to lose the most sleep over.

> Not Climate chaos/disaster, ecological+societal collapse, pollution?! Micro-plastics?

China's the leading driver of these things right now, by miles.

> Nukes?

You don't think nuclear-armed superpowers (like, say, China, Russia, and the US) butting heads might, you know, contribute to nukes being a danger in the first place? Or indeed, contribute to nukes being stockpiled in the first place?

The nukes being stockpiled again (or more, as the case may be) globally is the cause of a single country in that list.