When I was reading about this novel, before actually reading the novel itself, I read that it was an expose of the meat-packing industry in Chicago at the beginning of the 20th century - and I imagined that this meant it must be all about cruelty to animals and trying to persuade readers to become vegans. Well, no. Cruelty to animals is mentioned once or twice, briefly, in passing. The primary purpose of the book, however, is to persuade readers to become socialists, and the uncensored edition of the book isn't really so much an expose of the brutality of capitalism in the meat-packing industry as an expose of the brutality of capitalism everywhere, using the meat-packing industry as merely one particularly good example of it. The censored version, however, apparently cut out almost all suggestions that any industries other than meat-packing are in any way corrupt, and also considerably weakened the accusations against the meat-packing industry itself.
I think I should note here that I didn't entirely like this book; I generally like socialist politics well enough, but this book's tone of near-religious worship for socialism was a bit much for me at times. Bear in mind here that I'm normally someone who likes books that "hit the reader over the head" with a political message, and few things annoy me so much as the notion that literary merit requires that political messages be kept firmly obscured in endless subtleties. But this book . . . well, the entire final four chapters were not so much a "novel" at all as a word-for-word transcription of Eugene V. Debs' campaign speech as a socialist party candidate for U.S. president circa 1904! Or his speeches interspersed with various other prominent socialists' speeches, and the fictional main character of the novel contributing nothing but worshipful adoration of every word. I would have preferred some nuanced disagreement, with more room for readers to consider multiple points of view before being urged toward a final one. (Speaking of which, dis_senter happens to have just reviewed a different novel that does exactly what this one doesn't: presents socialism in a more complex way that neither condemns nor worships it.)
However, I've always said that hitting readers over the head with a political message can get the political message across more effectively than trying to be subtle about it, and the history of The Jungle (which doesn't contain even one halfway subtle sentence in the entire novel) seems to prove me right on this point. When the novel (the censored version of it) was published in 1906, Upton Sinclair mailed a copy to Teddy Roosevelt. Roosevelt, astoundingly, seems to have actually bothered reading it. (How much do you want to bet that the current U.S. president has never once read any book mailed to him unsolicited?) Roosevelt's less-than-encouraging reaction was to promptly write to the publishing company demanding to know why they would "publish such an obnoxious book as The Jungle," and quoting a report from the Agriculture Department that claimed the meatpacking industry was not guilty of the criminal practices described in the book. However, the publishing company and Upton Sinclair responded by presenting Sinclair's evidence, which led Roosevelt to realize that the Agriculture Department inspectors had been bribed to write a false report. Roosevelt launched an investigation, and soon, the public outcry against the meatpacking industry from other readers of Upton Sinclair's book became loud enough that it led to the passage of the first major U.S. Pure Food and Drug laws.
The sad part of all this is that the laws the censored version of the book led to, forbidding corporations to sell poisoned or improperly labeled food, only addressed issues that were really a rather minor part of what the original, uncensored manuscript of the novel had tried to call public attention to. The uncensored manuscript complained primarily about the corporations' mistreatment of their workers, and secondarily about the corporations' mistreatment of their customers by selling them unsafe meat. The censored version of the book, the only version available from 1906 until 1988, weakened the focus on the primary message and enabled lawmakers to get away with addressing only the secondary problem.
Anyway, it is a powerful book with an important history, and although the last four chapters did rather grate on me, the first thirty-two chapters didn't so much. It isn't the sort of book that you read for the joy of exquisite sentence structures, but it's a book that's almost guaranteed to open your eyes to a world that you weren't quite as aware of before reading it. Unless you've worked for the meat-packing industry, at least - and even if you have, you probably didn't work there in 1904, so you could at least learn how similar it was then to how it is now.