There exists an image of ideal-typical class struggle in the imagination of many a leftist: the working class, united across borders, fight against the capital-states. That has never happened, and that never will.
Jay Gould, who reportedly said, "I can hire one half of the working class to kill the other half," understood class struggle much better than any Marxist.
Class struggle in the real world is a cross-class political faction fight. When class struggle becomes revolutionary, it tends to polarize, pitting one faction consisting of peasants, workers, the petit-bourgeoisie from whom revolutionary leaders usually arise, and even a section of the bourgeoisie, against the other faction made up of peasants, workers, the petit-bourgeoisie, and the bulk of the bourgeoisie.
Why is it that revolutionary leaders tend to come from the middling sort? Because they are better educated and more ambitious than those below them and yet those above them block their advancement in the existing order. Only by destroying the existing order and establishing a new one can they make full use of their education and fulfill their ambition.
Their objective circumstances are not unlike those of Julien Sorel and Jude Fawley, but they are temperamentally Anti-Juliens and Anti-Judes: unlike Julien, they are not individualists; and unlike Jude, they are not defeated.
Intellectuals cannot become revolutionary leaders, however, unless the masses endow them with charisma. It is not intellectuals who choose the masses but the other way around. How the masses do so has been little studied by Marxists. For that, we must turn to Max Weber and Weberians, especially Pierre Bourdieu.