I think from my reading so far of the Devil in the White City, it showed that overcrowding was a really big issue in the 1880 or 1890’s. More and more people began to shift from living in the rural farm town and open areas to more of the populated and city like areas with more local shops and people. When the Chicago Fair came around even more people came flooding into the urban Chicago area which made it harder for police or local authorities to locate people who have gone missing. Like every other place, when a place has too many people to support, homelessness will begin to occur and more problems will arise as well such as not enough jobs.
I think Larson chose the Chicago fair to be intertwined with Holmes, the murderer, because that is when most of the innocent killings began to happen more frequently. The fair did a great job of attracting and bringing in many people so that also played apart for the overcrowding and made it harder to find missing people. The more variety of people also probably gave Holmes more of an open killing option and better ways to hide his tracks.