As Erik Larson explains in Devil in the White City, the World's Columbian Exposition marked a change in American culture. It was a time of great urbanization, and parts of Chicago were being rapidly constructed. It was also a time of dislocation and change, in part facilitated by the development of railroads. One of Larson's points is that people could get lost in a large city such as Chicago. Large cities were being constructed, but it took a while for municipal areas to catch up with the idea that their newly constructed cities needed stronger and more professional police forces.
Therefore, the World's Columbian Exposition was a dividing line with the past in many ways, as the fair marked a time of increased urbanization and anonymity in the cities. Larson's point is the new anonymity of cities helped create an environment in which crimes could be perpetuated.
At the same time, it was a crossroads in that the Industrial Revolution, which had started after the Civil War, accelerated in the late 1800s. Many new inventions came out of the fair, including spray paint and the dishwasher, along with the Ferris wheel and Aunt Jemima pancake mix. The fair showcased new forms of architecture built on a large scale. The fair marked the continued process of rapid industrialization in America.