The transition from slave society to feudal society is a struggle between the slave class and the slave owner class, from feudal society to capitalist society is a struggle between the feudal class and the bourgeoisie, and from capitalist society to socialism is a struggle between the bourgeoisie and the proletariat. These are the reasons for the revolution. The proletarian revolution is different, because capitalism liberates most of the productive forces, and the progress of human thought needs more equality and fairness. Therefore, to eliminate classes and create a society where everyone is equal, the examples I cited earlier are all social revolutions caused by class contradictions, which is also a law from low to high. Class struggle promotes historical development and social progress, and realizes the change of social form. Chairman Mao thoroughly expounded this truth: "We should dare to break the old world and be good at building the old world."