Complex sentence: The main candidates had headquarters at the Palmer House, which were often crowded as they served free alcoholic drinks--the Coliseum was located in a "dry" district of Chicago but the hotels were not.
Split into simpler sentences: The main candidates headquartered at the Palmer House, their rooms often crowded as they served free alcoholic drinks. The Coliseum was located in a "dry" district of Chicago but the hotels were not.