According to one of the lecture videos, marxists maintain that "the history of all hitherto existing society is the history of "

class struggle

Explanation:

Marx's draws on Engels view of history as a continuous dialectic process:

When Marx publishes his famous Communist Manifesto, he states "The history of all hitherto existing society is the history of class struggle.

This means that since the humans were able to organize in societies and organize for work, there will be a permanent fight between the ones who control the "surplus" and the ones who are active in working to keep the economy running. One dominant class and one dominated.

Throughout history, he identifies how this system came to existence first with slavery, then with feudalism, and went to the capitalist.

A permanent class struggle will follow as a historical and dialectical process.