You would be right to point out that, for example, there has been inequality for thousands of years, and we still have civilization (although local civilization

You would be right to point out that, for example, there has been inequality for thousands of years, and we still have civilization (although local civilizations/societies may have become extinct at least in part because of inequality building up in those societies). Of course, war has also been around for thousands of years, and has also destroyed various societies, but only within living memory have we had the war-making capability to destroy >99% of human life. (Whether that is a likely outcome if a nuclear war occurred is a separate question). Similarly the climate has changed before, but only in living memory have humans pushed the climate outside of its normal range of parameters, risking civilization-harming changes that happen faster than we can adapt to. In terms of inequality, what is perhaps new about the current age is the magnitude of difference between the poorest and the richest person. Some would say that the bottom 10% in the US are still richer in some sense than a king living 1000 years ago, and that may be true, but a modern billionaire is so much more wealthy than a modern poor person, that this level of inequality is arguably a difference of kind rather than degree. The precautionary principle would advise us that this new type of problem could cause a civilization-level danger, given how inequality has been associated with collapses in the past, and how large power imbalances tend to lead to corruption and abuse of that power. The precise mechanism for inequality causing the destruction of civilization is less clear than the mechanisms for war and climate collapse, but there are plausible ways that inequality can lead to the latter two, at least to a limited extent.