After examining the nature and history of the bourgeoisie, the Manifesto now turns to the proletariat. As the bourgeoisie developed, so did the proletariat, and it is the proletariat who will eventually destroy the bourgeoisie. The proletarians live only as long as they can find work, and they can find work only as long as their labor increases capital. They are a commodity, and are vulnerable to all the fluctuations of the market. Due to the development of machines and the division of labor, the proletarian's work has lost all "charm;" the proletarian is simply an appendage of a machine. Furthermore, as his work becomes more repulsive, his wage only decreases. Marx describes the worker as a soldier, and as a slave. Distinctions of age and sex are becoming less important as all people are simply instruments of labor. Furthermore, no sooner does the worker get his wages from his exploitative boss, then he is exploited by other bourgeoisie, such as his landlord.
The lower strata of the middle class, such as tradespeople, gradually sink into the proletariat. This is due to the fact that they lack sufficient capital, and the fact that technology has rendered their specialized skills no longer useful.
The Manifesto then describes the past history of the proletariat. As soon as this class was created it began to struggle with the bourgeoisie. This struggle originally involved the individual laborer, and later groups of workers, rebelling against the bourgeois that directly exploited them. These workers hoped to revive the medieval status of the worker. At this point, the workers were still disorganized, divided by geography and by competition with one another. Furthermore, when they did form unions, they were under the influence of the bourgeois, and actually served to further the objectives of the bourgeoisie.
However, with the modern development of industry, the proletariat increased in number, and became stronger and more concentrated. Furthermore, distinctions among laborers began to dissolve, as all shared equally low wages and equally unsure livelihoods. At this point, workers began to form trade unions and other associations, a process in which they are still engaged at the time of the Manifesto's writing. The proletariat is further helped in its unification by the increased means of communication made possible by modern industry, allowing for the struggles to take on national character. While the organization of the proletariat into a class is continually destroyed by competition among workers, each time it rises again stronger. Furthermore, as other classes try to use the proletarians to forward political their own ends, they give them tools to fight the bourgeoisie.
Marx explains that the only class today that is really revolutionary is the proletariat. All of the other classes that fight the bourgeoisie--such as the shopkeeper--are conservative, fighting to preserve their existence. Among the proletariat, however, the Old Society is already past preservation. "Law, morality, religion, are to him so many bourgeois prejudices, behind which lurk in ambush just as many bourgeois interests."
Historically, the proletariat are also unique. In the past, when a class got the upper hand, it tried to subject all of society to its own mode of appropriation. However, the proletariat lack any property of their own to retain or expand. Rather, they must destroy all ways of securing private property at all. Another unique characteristic of the proletariat is that, while past movements were started by minorities, the proletariats are a vast majority, and are acting in the interest of that majority.