The major historical reference on these pages is to the labor unrest of this time in American history and to the goals that the unions hoped to achieve. The Columbian Exposition was held only a few years before the “official” beginning of the Progressive Era in 1900, but there were of course progressive ideas already in circulation. Some of these are mentioned on these pages.
The progressives and labor unions wanted to curb the power of big businesses. They wanted to force the businesses to treat their workers better. On these pages, Larson mentions worries about the unions using the fair to push for minimum wages and the 8- hour day. He also mentions concerns about pollution and the sickness that could come with it. All of these things were issues that worried the unions and/or the progressives.
Thus, the major historical reference is to the demands that were being made by unions and progressives in the late 1800s.