Asklemmy

I'd disagree. If you look at the problems which create existential problems for "our civilization" (more on the scare quotes in a minute), the list is pretty short.

1. Nuclear war - This is existential to both civilization and to humanity as a species. Fortunately, this one is pretty easy to forestall: don't fucking do it. And that's actually been working out OK for the last few decades. For as insane of a system as Mutually Assured Destruction (MAD) is, it's also been pretty successful. Once every nation knew that using nuclear weapons in war meant everyone loses hard, they never got used again. Prior to that situation, they got used. And, there is no reason to believe that the US wouldn't have used them again, if the USSR didn't also have their finger on The Button. Sure, universal disarmament sounds like a better solution, but that also assumes everyone is willing to act in good faith. Just one bad actor and that all falls apart. And you can pretty much assume that there will be plenty of bad actors.

2. Climate Change - Depending on how bad this gets, it might rise to the level of "existential threat". But, most of the currently likely outcomes are probably not. This isn't to say they aren't bad and really horrific for a lot of people. But, even looking at something like a 2C rise over the next century, it's probably not going to cause the outright collapse of most major countries. Anyone not living in the US, China, India or a Western European country is fucked. Water shortages and famine in Sub-Saharan Africa are going to rise to levels completely unprecedented in history. But, from a question of "will society collapse"? The answer is "probably not". Though the surviving societies will only do so by accepting a mountain of corpses on their doorstep. And even some of the major countries might end up collapsed due to resource wars.

3. Astronomical Events - Throwing this in to avoid the "but actshuly" responses. Yes, if we suddenly discovered a big ass rock headed our way, we're likely fucked. Also, if we get caught by a massive gamma ray burst, we're all gonna get turned to jerky. But, these are so low likelihood events as to not be worth worrying about.

Other than that, there isn't all that much which could really wipe out all civilization, everywhere, at once. And this is where I get back to those "scare quotes". We don't really have one single civilization on Earth. We have a bunch of them which interact in lots of ways. While that interdependence does make things a bit fragile, it also means that there is a higher degree of redundancy. If the US went tits up tomorrow, it would have some major impacts on China, India and Western Europe. But, each of those areas has a reasonable chance of adjusting and and continuing on. There may be a lost decade or three while supply chains adjust and new infrastructure is built out, but there is nothing wholly unique to the US which couldn't be replicated elsewhere. And depending on how the US failed, the useful bits of the US economy might well be able to be rebooted by someone else. Again, there is probably a lot of death on the table, the US is a major food exporter, after all. But, China already has a history of weathering millions of people dying to famine, I'm sure the PRC government could figure out a leap forward. An with such useful farmland in the US, one would expect farms to pop back up and get producing pretty quick. Maybe not at the level of output which the US currently has, but if we've killed off half or more of the US population, then we have a bunch of useful farmland with a lot less people to feed.