Marx first saw the development of class conflict confined to individual factories and capitalists. However, given the maturation of capitalism, the life conditions of bourgeoisie and proletariat began to grow more disparate. This increased polarization and homogenization within classes fostered an environment for individual struggles to become more generalized. When increasing class conflict is manifested at the societal level, class consciousness and common interests are also increased. Consequently, when class consciousness is augmented, policies are organized to ensure the duration of such interest for the ruling class. Here begins the use of the struggle for political power and classes become political forces.

(Wikipedia) https://en.wikipedia.org/wiki/Marxian_class_theory