A Thought on the French Bourgeois Revolution specifically because I was reading about it when this occurred to me.
I think a really important aspect of the French bourgeois revolution was the formation of institutions that lead to a feeling of entitlement within the oppressed classes. Property ownership in the peasant class is a good example.
Land ownership (at least for myself) breeds a sense of power and of my place in the world. I view the place I am currently sitting as my house, in the back yard is my garden, on my property and I would fight to the death to protect that (I dare you to test me on this Dan).
Serfs, or slaves, or whoever, that feel that they are in their "proper" or "god given" or predestined place in the world will not start a revolution. It is only when there are feelings (arguably determined at least in part by the existing institutions in society, be they cultural, economic or political) that lead to a sense of being entitled to more than a person currently has, or treatment better than what is currently being recieved, that revolution becomes a possibility.
People will not act in a revolutionary fashion if they feel that everything is as it was meant to be.