alt Hacker NewsThe world war helped via wealth destruction and redistribution. Polybius' theory also has Arabic (Khaldun) and Chinese analogues. In China it looks like a 300-ish year cycle driven by wealth/land concentration and elite corruption which ends with peasant revolts, a power vacuum, peasants taking back their own land, and a new dynasty formed by rebels or invaders, after which the new elite slowly begins encroaching on the peasants and taking their land again.
The idea that wars, epidemics, and catastrophes lead to wealth redistribution is the thesis of "The Great Leveler" by Walter Schneidel: it's not an absolute rule (and as far as I remember, another book was published to criticise this one), but it seems to hold through a change in power dynamics, supply and demand of labour, and coordination between the previously oppressed classes.