On Revolutions(Especially the French, Russian and Chinese)

Revolutions signal a massive and developmental political challenge and change. We'll mostly talk about the Russian, French, and Chinese revolutions. Thinkers we'll talk about are Theda Skocpol, Rousseau, Richard Pipes, Karl Marx, and more. You can also talk about other revolutions or similar overthrows in South America, Vietnam and Africa. Are there pre-literate overthrows? Do books play a major role in facilitating overthrows. To some extent the fall of the Romans was a pre-literate(at least of mass literacy) overthrow. So thinkers like Gibbons can be discussed. What makes revolutions happen, a wholesale deterioration of the old order or other shocks like crop failure, marxism, and genuine malcontent?