One needs not embrace Marxist views to see the importance of class in understanding political behavior of actors. See Aristotle's Politics book 4, 5, and 6--or the whole Italian School of Michels, Mosca, and Pareto.
''all history is the history of class'' was a rhetorical exaggeration in a text designed to wake up its readers. Marx's later studies 1) recognized that exaggeration and looked seriously at early non-class societies and 2) by postulating emerging communism as both the abolishing classes and humans-beginning-to-make-their-own-history, that simple rhetorical statement was substantially superseded.
The concept of Marxism claims in all history is the history of class suggests that throughout history, conflicts and developments can be comprehended through the lens of social classes.
In other words, it declares that the interactions and the agitation between diverse social classes are the driving force behind the historical evolution and development.
All history is the history of class struggles," a fundamental principle of Marxist theory, posits that the driving force behind historical development and societal change is the conflict between different social classes. According to Marxism, this conflict arises from the inherent inequalities in the modes of production, where the ruling class (bourgeoisie) exploits the working class (proletariat). This struggle for economic power and control over resources shapes the social, political, and economic structures of society. Marxists believe that history progresses through a series of stages, from feudalism to capitalism, and ultimately to socialism and communism, each characterized by a distinct class struggle that drives transformation and development.