What about food security and the price of food? I recall seeing that's generally the ultimate catalyst for revolutions, cf French cake and the price of tea for wannabe ex-Brits ;-p

I believe this also featured in the Arab spring. When asking Zimbabwean colleagues 15 years ago why people hadn't risen against Mugabe yet, they told me that while people still had food they would bear the yoke.

This theory is highly generalized. Depending on context any critical resource may become precious as a result of economic problems and social disparity. Sometimes it is food, other times housing, and so on. And these triggers are differentiated from the structural issues that generate critical instability in the first place. What spreads kindling around may be unrelated to what strikes the match.