Chicago became one of the most rapidly growing, industrialized cities in America in the Gilded Age. With it's industries booming, its rapid growth led to an equally rapid rate of change, an almost sped-up exaggerated view of the consequences of industrialization and nineteenth century change.
Chicago experienced a high rate of immigration, and with immigration becomes high populations which in turn give rise to a whole manner of new issues. Crowding, leading to the heavy use of skyscrapers, as limited land meant having to build "up" instead of "out," crime, which was naturally rampant under these circumstances, and a lack of hygene, also directly impacted by these living conditions. While this occurred all over America, Chicago was the highlight of this change, as it experienced economic, industrial, and social change at a much higher rate.
However, Chicago took larger measures to remedy these problems, advancing quickly in the creation of proper sewage systems and stylistic, as well as functional skyscrapers. With the hosting of the Worlds Fair in Chicago, later, the eyes of the world settled in on this booming city. With its over the top displays and amusement and the overall girth of the city itself, the wealthy, and the usually white, flowed in and gave this booming city even more attention. It wouldn't be unwise to say this large amount of attention on an already socially, economically, and industrially booming city is what would allow it to be considered the "sample" of America, the whole.