In 1890, St. Louis was the 5th largest city in the United States (after NY, Chicago, Philadelphia, and Brooklyn which was considered separately).  It was the hub for traffic from the east going west and south along the Mississippi and Missouri rivers - and lots of traffic could only be transported over water.  By 1900, Brooklyn was considered part of New York City, and so St. Louis became the 4th largest city in the U.S.  When the American League was formed in Baseball in 1901, five cities had teams in both the National and American leagues, and they were situated in the five largest cities in the country: New York, Chicago, Philadelphia, St. Louis, and Boston.  And in 1904, St. Louis hosted a world's fair.  In short, when your great-grandfather came to the U.S., St. Louis was a large bustling growing metropolis with lots of opportunities for jobs and filling the American dream. 

Zalman Usiskin