What is the the theme of the novel Coolie by Mulk Raj Anand?

Mulk Raj Anand's 1936 novel Coolie is about a 14-year-old boy, Munoo, who represents the lowest part of India's socioeconomic spectrum, a position identified by various names, including Dalit and, more commonly, "the untouchables." They are destined to remain at the bottom of this extraordinarily rigid caste system.  By presenting as his protagonist a servant in the home of a member of the upper caste, the desperately poor Munoo, Anand has indicted the entire class system that dominates Indian culture.  Furthermore, by vividly contrasting the opposite ends of the socioeconomic spectrum through the eyes of his perceptive protagonist, the author has illuminated the fundamental injustices inherent in the system imposed by an alien power, Great Britain, while also placing the blame for this unfortunate situation squarely in the hands of those Indians on the higher levels of the socioeconomic spectrum (one cannot use the phrase "socioeconomic ladder," as that would denote the possibility of upward mobility). The latter have benefited from this system while ignoring its long-term ramifications.  In one passage in Coolie that presents this stark contrast between the hopes and expectations with which the individual is raised in Indian society, Anang describes the young boy's thoughts:

"It did not occur to him to ask himself what he was apart from being a servant, and why he was a servant and Babu Rathoo Ram his master.  His identity he took for granted, and the relationship between Babu Rathoo Ram, who wore black boots, and himself, Munoo, who went about barefoot, was to him like sunshine and sunset, inevitable and unquestionable."

The theme of Coolie, therefore, is the hopelessness and despair to which millions of Indians are condemned by virtue of an antiquated and inherently unjust economic and social structure.