Modern Era (since 1900)

Definition

Through the year 1900, MLB was composed of various leagues that are no longer active, as well as the National League, which was established in 1876. The American Association (1882-91), the Union Association (1884) and the Players’ League (1890) are the other officially recognized major leagues from that time period.

The American League was founded in January 1901, and two years later, the champions of the American and National Leagues met in the first World Series. The 1903 World Series was a matchup between the Boston Americans (AL) and the Pittsburgh Pirates (NL), with Boston winning the then-best-of-nine series in eight games (the Fall Classic became a best-of-seven series in 1905).

For much of the Modern Era, the AL and NL have been the only two leagues in Major League Baseball -- with the exception of the Federal League from 1914-15, and the Negro Leagues from 1920-48.