I know US history education isn't greatest but you might have heard about French revolution, rise of Nazism or various communism uprisings, Mexican revolution in 1910s.
With better outcomes for society: labor movement at the turn of century and in 30s.
French revolution for one was not about income inequality per se. It doesn't seem the idea itself was in people's mind - and too many other issues instead.
If the French revolution wasn't about income inequality then there has never been a conflict about inequality... Read the Rosseau and Voltaire of the period leading up to the crises. You can feel their passion when they talk about inequality.
"The rioters had already availed themselves of the stores of the Hôtel de Ville, but they remained unsatisfied: they wanted not just one meal but the assurance that bread would once again be plentiful and cheap. Famine was a real and ever-present dread for the lower strata of the Third Estate, and rumors of an "aristocrats' plot" to starve the poor were rampant and readily believed.[2]"
Not about income equality per se, but you know, not wanting to starve in the streets. Lol what the fuck.
You negate your own critique: "assurance that bread would once again be plentiful and cheap".
So like I say "inequality" doesn't even enter the broad collective mind. And the intellectuals that try to run "what's next" do talk about "égalité" but again that's not what they mean.
This is not what anyone means by "inequality" now. Not killing the economy with random wars, yes. Welfare, yes. Price controls even, sure. Better planning (because we are talking about famines here in this specific case - not even taxes.) Even when "Egalité" and "Fraternité" make it into foundational texts, soon after, this is not what they are about.
I think it's a big stretch to point to all of those and say wealth inequality is the main reason all of those happen. For example, people were starving around the French revolution. With Germany I believe it was just as much (if not more) general depression and national embarrassment rather than wealth inequality. With Arab Spring you can point to poor leadership as opposed to innate wealth inequality. I'm not convinced wealth inequality is the underlying reason.
Just open Wikipedia man. It has citations to primary sources.
"Although the 18th century was a period of increasing prosperity, the benefits were distributed unevenly across regions and social groups. Those whose income derived from agriculture, rents, interest and trade in goods from France's slave colonies benefited most, while the living standards of wage labourers and farmers on rented land fell."
Same for Arab spring, it's like second sentence on the wiki. It's also heavily about corruption, but guess what, those two go hand in hand. Open maps for corruption and Gini index and you will see strong correlation.
Of course there are more reasons. Society is complex.
https://www.nytimes.com/2020/07/01/opinion/economic-inequali...
https://www.washingtonpost.com/news/wonk/wp/2018/02/06/how-r...
https://time.com/6267552/falling-american-inequality/