It all comes back to effective education. The uneducated are idiots, willing to cut their own throats if somebody they think knows more than them tells them it's a good thing.
The more educated a society is, the less likely it is to rip itself apart.

I'd think there's kind of a tripod for social stability involving education, economic prosperity, and personal identification/investment in the status quo. You can probably pull one leg right off the tripod and have things still work out, but start pulling two or all the legs off and it's going to end in trouble.

In the US and western Europe in the 60s and 70s you had a lot of people who did not feel any personal affiliation to the status quo, but that by itself was not sufficient to generate revolutionary sentiments on a widespread enough basis to lead to serious problems. Conversely, in post-WW1 Germany you had economic implosion and people who felt alienated or hostile to the government imposed on them the winners of the war (and/or their government that had lost them the war) -- about the only thing left was a well educated population, who then elected Hitler.

mmmm I'll take a GDF-005 35mm.