Naked Capitalism has the article Democracy and the Threat of Revolution: New Evidence.
Some theories suggest that the threat of revolution plays a pivotal role in democratisation. This column provides new evidence in support of this hypothesis. The authors use democratic transitions from Europe in the 19th century, Africa at the turn at the 20th century, and the Great Reform Act of 1832 in Great Britain. They find that credible threats of revolution have systematically triggered pre-emptive democratic reforms throughout history.
I guess we are going to have to come up with something more credible than the Occupy Movement.
The article mentions one effect that I have always felt was important.
There are many reasons why droughts might lead to riots; for instance, the temporary reduction in income lowers the opportunity cost of contesting power,
In other words, if people have sufficient opportunities to prosper without revolution, then they will not rebel. However, when the oligarchs remove every avenue to prosperity for enough people, then they have nothing left to lose if they rebel.
Janis Joplin, that great philosopher, had it right.