How does Marx summarize the bold portion of paragraph 1?

The Communist Manifesto begins with Marx's famous generalization that "the history of all hitherto existing society is the history of class struggles" (79). Marx describes these classes in terms of binary oppositions, with one party as oppressor, the other as oppressed. While human societies have traditionally been organized according to complex, multi-membered class hierarchies, the demise of feudalism effected by the French Revolution has brought about a simplification of class antagonism. Rather than many classes fighting amongst themselves (e.g. ancient Rome with its patricians, knights, plebeians, and slaves), society is increasingly splitting into only two classes: Bourgeoisie and Proletariat.