When I was at uni I read Thomas Piketty's "Capital in the 21st Century", and parts of his newer "Capital and Ideology" (although I never quite got through that one).
The big takeaway for me was that wealth inequality never improves without some major catastrophe (war, revolution, plague etc). The proposed model is really intuitive and compelling (tldr; return on capital has historically always been higher than real growth, which guarantees indefinite concentration of wealth until there's a crisis).
Last year's Nobel Economics Prize winners, Acemoglu and Robinson, tell a similar story in "Why Nations Fail", which I am working through at the moment. Although in their case, they seem be suggesting a more causal link between erosion of political and economic institutions and the collapse of empires.
I wish these ideas were more broadly accessible and understood. The real risk of total societal collapse should transcend any partisan fighting about ideal tax rates, government inflation/unemployment targets etc. Everyone has a common interest in there not being a violent upheaval (arguably the rich most of all).
Last I checked the numbers, current wealth inequality seems about as bad as it was before the great depression. And its not enough to just say "well, absolute wealth is more important". As others have pointed out, its not stable to have such huge relative wealth disparities. And that's before you even consider corruption.