The National League and the American Association went to war in 1891 over the reassignment of ex-Players' League players. The American Association attempted to raid former National Players and bring them to the horribly underwhelming AA. The American Association pulled out of the National Agreement, an old AA/NL agreement which recognized the AA as a major league in return for the AA ceasing to raid NL rosters for talent.
The 1891 season was a constant struggle between the two leagues for dominance, and finally, by the end of the season, the American Association folded. The National League purchased four American Association clubs and admitted them to the National League. It bought off remaining teams for $130,000.