If we are worried about risks, one valuable question is whether there have been historical analogues and/or near misses.
Related Posts: Pawntoe4's On Collapse Risk (C-Risk), landfish's Update on civilizational collapse research, MichealA's Sources on Civilizational Collapse Risks, and Denkenberger's Loss of Industrial Civilization and Recovery (Workshop)
Can civilizations collapse? (Yes.)
Local collapses have long-occurred, from the collapse of Mesopotamia more than four millennia ago, due to drought and agricultural failures, to the decline of Greece, due largely to political infighting, to the fall of the Roman, Ghanan, Malian, or Songhai Empires, each due to a combination of politics, economics, and external invasions. In each case, the populations suffered, many died, and none ever recovered their pre-eminence. This seems like an obvious catastrophe, but short of an existential risk.
However, a collapse like that of the Roman empire has effects that last for centuries even when recovery occurs. The recovery came slowly, despite the Merovingians, then Carolingians, then the Holy Roman Empire and the Muslim world attempting to continue or build upon various parts of Roman civilization and scholarship. Global civilization could easily fall far more precipitously, with even less ability to recover.
How Frequent are Collapses?
This is unclear, and plausibly important. Luke Kemp at Cambridge CSER has a short review of ancient civilizations, which seems fairly useful at getting a better handle on this. It seems unclear how often these were supplanted, conquered,
What does this imply about Modern Civilization?
Modern global civilization is more robust to many types of failure, more unified, and in some ways more fragile. A local collapse could be contained, as happened after the devastation of Europe during World War Two, or the former Soviet block after the fall of communism. In each case, the shock was absorbed by the larger global economy, and the local impacts were drastic and lasted decades, but the decline in living standards was short term, on the order of a single lifetime, and it seems clear that global progress more than compensated in the medium term.
A global collapse, however, would plausibly leave no outsiders or successors to pick up the baton, as Rome did for Greece. The lack of successors to pick up the pieces, along with the availability of weapons that could wipe out all human life, and global-scale threats like climate change, makes a modern collapse far more dangerous for humanity's future.
Afterwards: These are some notes from a paper which were cut, but I think they are worth presenting, simply as a reminder that collapse isn't as rare as we might assume. It also seems worth building more understanding around the cases which occurred in the past - I'd be happy to see people do more work on this, and this seems like a great place for a non-technical undergraduate student to make a significant contribution.
(I think this comment isn't important for the core points of this post.)
Do you mean "an obvious catastrophe from the perspective of the regimes that had ruled those civilizations"?
I think it's not obvious that all/most societal collapses in history have been catastrophes from the perspectives of those society's populations, let alone the perspectives of the world. See, for example, the book Against the Grain, which:
(Though we could theoretically accept the latter view and yet still think collapses were negative for the people in those societies, because of the related turmoil.)
But this is mostly a nit-pick/tangential query, because:
This was imprecise - I meant that collapses were catastrophes for the civilizations involved, and current collapses would also be catastrophes, one which I agree would be significantly worse if they impacted humanity's longer term trajectory. And yes, some collapses may have been net benefits - though I think the collapse of early agricultural societies did set those societies back, and were catastrophes for them - we just think that the direction of those societies was bad, so we're unperturbed that they collapsed. The same would be said of the once-impending collapse of the antebellum South in the US, where economics was going to destroy their economy, i.e. slavery. But despite the simplicity of the cause, slavery, I will greatly simplify the political dynamics leading to the outbreak of the civil war and say that they started a war to protect their culture instead of allowing the North to supplant them. This seems like a clear civilizational catastrophe, with some large moral benefits from ending slavery.
I think that unlike the Antebelllum south, and early exploitative agricultural societies, the collapse of Rome was also a collapse that hurt civilization's medium-term trajectory, despite taking quite a long time. And I'm hoping the ongoing collapse of the post-WWII international order isn't a similar devolution.