Hello! A couple friends of mine wanted me to run an alt-history game taking place in Chicago in the 30s. I know I want organized crime involved, so I want to have a good understanding of organized crime, its causes, its major events, its major characters, etc. Any good book suggestions?
Any biography of the major figures of the period--Al Capone in Chicago is probably the most relevant to you--will help with the details.
I can also suggest the writings of Virgil Peterson, who was an FBI special agent and the director of the Chicago Crime Commission, a civic group that, true to its name, kept (and keeps) track of crime in the Windy City. If you are looking for a book, I would suggest his Barbarians in our Midst - A History of Chicago Crime and Politics .
You may also want to look at a series of articles that he published in the 1940s that are available via Northwestern University's scholarly commons. I particularly recommend "Chicago's Crime Problem," in which Peterson sketches a brief history of Chicago crime going back to the 1870s.
Game sounds like a lot of fun! Best of luck with it.