Your local library probably has a copy of Nature’s Metropolis, a very well-written, information-dense book that captures much of the reason why it was Chicago rather than, say, St. Louis that became the important link in the railroad system. (In the mid 18th century France and the UK concluded a treaty that made the ‘Illinois Country’ off-limits to Europeans. It depopulated and most people moved to St. Louis. By the time Chicago was much more than an Army fort and a dozen houses, St. Louis was a 100-year old large city).