A few words on my personal theory of history.

Societies begin within a competitive environment in which only a few societies survive, namely those involving internal cooperation to get wealth. The wealth can be produced, exploited, realized through exchange, and/or taken outright from others. As the society succeeds, it grows, and the incentive to cheat the system of cooperation grows. Mutual cooperation decays as more selfish strategies become better and better - also attitudes towards outgroups soften from those that had led to ascendance. Eventually a successful enough society will have wealth, and contain agents competing over its inheritance rather than creating new wealth, and people will move away from social codes benefiting the society to those benefiting themselves or towards similar luxuries like believing things because they are true rather than useful.

Within this model I see America as in a late stage. The education system is a wasteful signalling game because so much wealth is in America that fighting for a piece of the pie is a better strategy than creating wealth. Jingoism is despised, there is no national religion, history, race, or idea uniting Americans. So I see present effort as scarcely directed towards production at all. Once GNP was thought the most important economic statistic, now it is GDP. The ipad is an iconic modern achievement, like other products, it is designed so consumers can be as ignorant as possible. Nothing like it needs to be produced - all the more so reality TV, massive sugar consumption and health neglect, etc.

A new society would begin in a productive, survivalist mode, but with modern technology. Instead of producing Wiis and X-Boxes, I think a post nuclear society would go from slide rules to mass transit and solar power in no time, even with a fraction of the resources, as it would begin with our information but have an ethic from its circumstances. The survivalist, cooperative, productive public ethos would be exhibited fully during an internet age, rather than after having been decaying logarithmically for so long.

Not at all. Most bad things aren't existential risks.

Bad things are not vulnerable to every argument, nor are they bad because they make absolutely every metric of negativity worse, but because on balance they make things worse. Good things are not validly supported by every possible argument, nor are they good because they improve absolutely everything, but because they are on balance good.

Nuclear war isn't bad because it alters the laws of physics to make atmospheric nitrogen turn into Pepsi. Nor is it bad because it is an existential risk. It has little to do with either of those things.

Preventing nuclear war isn't good because it's a D&D quest where satisfying certain conditions unlocks a bag of holding that solves all landfill problems forever. There isn't such a quest. Preventing nuclear war is still a good idea.

Arguments in favor of preventing nuclear war mostly fail, just like arguments for any conclusion. You can't get away with writing a warm and fuzzy conclusion such as "prevent nuclear war" as your bottom line and expect everyone to just buy whatever argument you construct ostensibly leading to that conclusion.