Complex sentence: The St. Louis Cardinals, a Major League baseball (MLB) franchise based in St. Louis, Missouri, have competed in the National League (NL) since 1892, and in the American Association (AA) from 1882 to 1891.
Split into simpler sentences: The St. Louis Cardinals, a professional baseball franchise based in St. Louis, Missouri, compete in the National League (NL) of Major League Baseball (MLB). Prior to entering the NL in 1892, they were also a member of the American Association (AA) from 1882 to 1891.