[not_jd_salinger]

Can you please list some of this "far worse situations" than nuclear war and climate change as we are currently facing?

"Societal cohesion" doesn't do too much to help us survive crop failures and wet bulb temperatures over 35C.

Aside from that, I think you might misunderstand your causal arrows a bit. It is fair more likely that massive industrialization and late state capitalism led to a society that valued the individual over the social unit, rather than that a sudden desire to be individuals sprung up in people's hearts and made a mess of the world.

[ceilingcorner]

Black Death and Mongol Invasions were probably worse on a per-person basis for those affected than even a realistic nuclear war would be.

[sudosysgen]

Absolutely not, not even close. 99.9% of the population dying within a few years is not comparable to a disease that killed ~10% of the population and a series of invasions that killed at most a single percent.