Over at Smithsonian.com there’s a good write-up on the Chicago Fire. Today is the 142nd anniverary of the disaster. If you’re not aware of it, Mrs. O’Leary was very belatedly exonerated for starting the fire.
If somebody asked me (which nobody has), I’d say the real causes of the fire were too many wooden buildings, bad city layout, inadequate city services, and the weather. Without those, working synergistically, the fire which destroyed 2,000 acres of Chicago, would have been contained easily.