Founded as a small trade outpost and becoming incorporated as a small municipality in the 1830s, the population of the city of Chicago exploded making it the second largest in the United States by 1890, fifth largest in the world and largest (by far) in terms of cities that did not exist at the turn of the 18th Century.
Thanks in large part to its central location in the country connecting the East to the West through the Great Planes and the North to the South via the Great Lakes and the Illinois and Michigan Canal to the Mississippi River, the city's economy thrived as well. Chicago became the United States' domestic shipping and railroad hub.
In 1871, the city burned to the ground in the Great Chicago Fire. Although tragic, this clearing of ground allowed for Chicago to become one of America's first planned cities, following Daniel H Burnham's plan to make the city highly dense, but livable, efficient and replete with lake shore park space. Additionally, the massive construction that took place made Chicago one of the major centers of modern architecture, taking off in Beaux-Arts and Neoclassical splendor and being home to several of the earliest skyscrapers. The plan and it's new architecture made it reminiscent of 19th Century Paris and won it the nickname "Paris on the Prairie."
Chicago's population reached its peak of 3.6 million in the 1950s, and thereafter it was hit hard by "White Flight" and migration to the suburbs. After being the nation's second city for around a century, its population was surpassed by Los Angeles at some point in the 1980s. Despite this, it still remains the U.S.'s #2 influential economy and "Chicagoland," Chicago's greater metropolitan area, is one of the fastest growing metro-areas for metro-areas with over 5 million people and an enormous center of commerce (GMP $5.2 M).
The challenge: with an earliest POD of 1860 (although I recommend not butterflying away the Great Fire), make Chicago (currently OTL 2.8 M people, GDP 5.2 M) have an equal or greater size and economy of modern day OTL New York City (8.2 M people, GDP 1.2 T) that is regarded as the cultural and financial capital of the United States and by extension one of the foremost cities in the world by the year 2000.
What do you think?
Possibilities include:
- Special role during a war with Britain where coastal cities were bombarded or blockaded
- A greater role for the U.S. train system
- A more exact realization of Burnham's plan
- Greater appeal of the 1920s gangs to immigrants
- Lessened effects of great depression
- Special role during World War II (beside center for Manhattan Project)
- Less incentive to move to suburbs post-War than in other cities
- ???