I think there was not just one catalyst. I do think MbS is hoping to soften them up, and they just finished beating ISIS there. More than one spark, in what was already as I describe a powder keg.
Iran is worse due to sanctions. China and Russia were working to stabilize them economically, but with ISIS and how strong the structural issues are, it was just a start not felt outside a few business owners. But Iran is far from unique in the region. And inequality combined with a large cohort of resentful and un/underemployed young men with no prospects is always a recipe for this. This is part of why el-Sisi has been speaking out about MbS’s actions as destabilizing, he sits on another one of the powderkegs of resentment. There are many more, not all in the Arab/Persian world. “Arab Spring” isn’t over, it failed to achieve anything meaningful. There were many reasons, but the result takes me here:
“Those who make peaceful revolution impossible will make violent revolution inevitable.”
Not that I expect violent revolutions to achieve meaningful progress either, certainly almost never in the short run. But they usually aren’t about that, they are about stopping pain by sharing it. From my reading, in the longer arc of history, the high levels of inequality are most often fixed by violent revolution and war. I’d prefer taxes, but that also relies on a government that is less corrupt. Inequality also breeds corruption, and it certainly weakens and degrades the quality of a democracy. So even that is a race. One usually lost, again, historically. Still, I’d prefer we go that way. I realize I say this against the backdrop of the recent tax bill.