Why did Sinclair assume the events of the book would portray the need for Socialism in early 20th century America ?

Sinclair was exposed to Socialist politics as a young writer and quickly became convinced by the movement's premise. Socialism is an economic theory that promotes worker ownership of the resources of production. Sinclair came to see capitalism as a vicious system of economics that exploits the masses in order to make the elite few rich. Capitalists hoarded resources and wealth for themselves, while millions of workers and laborers suffered in poverty and dangerous working conditions.

Sinclair conceived The Jungle as a Socialist novel. The plights of the novel's protagonists demonstrate the evils and corruption of unrestrained capitalist economies. Jurgis and Ona Rudkus, as well as their immigrant friends and family, live in dire poverty. Their lives are at risk when they go to work, if they are able to find work. These conditions are the result of a company that seeks to maximize the speed and efficiency of labor with no regard to how such methods of production affect the lives of workers. The novel is a sustained argument that workers must gather collectively in order to assure rights and dignity for all individuals.