The league was founded in September 1883 by the young St. Louis millionaire Henry Lucas. Lucas was eventually named the league's president. Lucas' favoritism toward his own team doomed the league from the beginning, as he acquired the best available players for his St. Louis franchise at the expense of the rest of the league.
The lopsided competition, the revolving-door nature of the franchises and the poorly drafted schedule was also a major problem; four franchises folded during the season, forcing the league to scramble to replace them with three teams from lower classification leagues and one new team, and the league was derisively dubbed "The Onion League" by its detractors in the two established leagues.
Although the league is conventionally listed as a major league, this status has been questioned by a number of modern baseball historians. The league had a number of major league players (on the St. Louis franchise, at least), but the league's overall talent and organization was notably inferior to that of the two established major leagues at the time. The Union Association folded in at the end of 1884, its first and only season.