Marx was not a future teller. The revolutions are, indeed, caused by class struggle, but we learned trough time that to occur, a revolution need some objective and subjective conditions. (Lenin) The revolutions we experienced happened mostly on underdeveloped countries, contradicting Marx’s previsions.

The most developed economies tried to minimize it’s contradictions home, while exporting them to other countries, (also Lenin, Imperialism) avoiding the development of subjective conditions to revolution. (Henry Ford and Keynes play a crucial role here)

After the colapse of USSR neoliberalism put a end on this policy, and now we see a surge of revolt on developed countries because of the increasing contradictions under neoliberalism.

Not every revolution is successful.

We fixate on leaders for simplifying our study of history but there is a lot of groundwork to be laid for a revolution to gain momentum before it can cross the hurdles from the ruling class it encounters. A good example is the situation in Bolivia. It wasn’t just about getting Evo Morales elected into office but the mass support and organising from the working class that made MAS’ rise to power successful so that it could withstand a coup attempt backed by the US even after many of the supporters were murdered (even some party officials) by coup government. Lenin has said that revolutions don’t occur spontaneously. It’s a conscious action of a society to reorient itself which is why a vanguard party is important.

Revolution doesn’t purely mean guns or the over throw of power necessarily. The industrial revolution for example. Marx himself realized that this was ongoing. Communists don’t really aim for revolution but are aware that revolution in the decisive sense (violent seizure of power) will be necessary. The very nature and existence of the working class, as the antithesis of the bourgeoisie means that it is the working class that will cause these revolutions in society. As the working class struggle, the bourgeoisie are forced to change things that increasingly phase them out and make them useless. Every massive change in capital was caused because of class struggle.

if the syetem (economic) has multiple critical flaws, these could be: extreme wealth difference, (class) extreme courruption causing civil unrest, (rebelion) could be caused by lack of law enforcement and starvation. Ect. this was off the top of my head.