Officially known as American League of Professional Baseball Clubs
The American League has its origins in the minor league Western League, which existed from 1894 to 1899. The league was reorganized and renamed by Ban Johnson in 1900 and played as a minor league that year. Its intention, however, was to compete with the National League, and it did so in 1901 when it proclaimed itself a rival major league, moved teams into the cities of Boston, MA and Philadelphia, PA, even though they were occupied by National League teams, and started to sign NL players. In 1903, with a precarious peace established through the National Agreement, the champions of the rival leagues met in the first World Series. In 1904, though, there was no World Series due to the refusal of the New York Giants to play along; public pressure forced a permanent peace between the leagues after that, but the leagues remained distinct entities with their own presidents.
The leagues maintained their own umpiring crews, with the American League home-plate umpires continuing to use outside chest protectors for decades after the National League umps had phased them out. With the outside protector the American League umpires stood further back than National League umps. This positional difference, and the perspective on the strike zone it lent, may have led to what was perceived as a difference in pitching styles of the two leagues from mid-century into the free agency era, that the National League was a fastball league where pitchers would "challenge the hitter" whereas the American League was a "breaking ball league".
In 1973, the American League introduced the designated hitter to official big league games. In 1999, the two leagues were virtually dissolved as the league presidencies were abolished and merged under a single commissioner in Bud Selig, and the two leagues' umpire crews were commingled. The AL (as it's frequently called) now exists in name only as part of Major League Baseball. The American League is often called the "junior circuit", given it is 25 years younger than the National League.
- Ban Johnson: (Oct. 11, 1899) to (Jan. 23, 1927)
- Frank Navin: (acting) (Jan. 23- Apr. 23, 1927)
- Ban Johnson: (Apr. 23-Oct. 17, 1927)
- Frank Navin: (acting) (Oct. 17-Dec. 13, 1927)
- Ernest Barnard: (Dec. 13, 1927 to Mar. 27, 1931)
- Frank Navin: (acting) (Mar. 27-May 27, 1931)
- Will Harridge: (May 27, 1931 to Dec. 3, 1958)
- Tom Yawkey: (acting) (Dec. 3, 1958 to Jan. 31, 1959)
- Joe Cronin: (Jan. 31, 1959 to Jan. 1, 1974)
- Lee MacPhail: (Jan. 1, 1974 to Dec. 8, 1983)
- Bobby Brown: (Dec. 8, 1983 to June 8, 1994)
- Gene Budig: (June 8, 1994 to Jan. 6, 2000)
The separate league office was eliminated in 2000 with the merger of the two leagues under the Commissioner's office, although the Commissioner named an honorary league President whose duties are purely ceremonial.
- The World Series was played in a best-of-nine format
- The New York Giants declined to play the American League champions; there was no World Series
- Won one-game playoff against Boston Red Sox
- The season was shortened by a strike; a special postseason format was used
- The season was ended by a strike and the postseason was cancelled; the Yankees had the best record in the league when the season ended
- The season was shortened by the coronavirus pandemic; a special postseason format was used
- Russell Schneider: The Cleveland Indians Encyclopedia, Temple University Press, Philadelphia, Pa © 1996
- "Frank Robinson named Senior Advisor and Honorary A.L. President", mlb.com, February 2, 2015. 
- Paul Hensler: The American League in Transition, 1965-1975: How Competition Thrived When the Yankees Didn't, McFarland, Jefferson, NC, 2013. ISBN 978-0-7864-4626-1
- Donald Honig: The American League: An Illustrated History, Crown Publishers, New York, NY, 1983. ISBN 0517550423
- Michael T. Lynch, Jr: Harry Frazee, Ban Johnson and the Feud That Nearly Destroyed the American League, McFarland, Jefferson, NC, 2008 .
- Robert Kuhn McGregor: A Calculus of Color: The Integration of Baseball’s American League, McFarland, Jefferson, NC, 2015. ISBN 978-0-7864-9440-8
- Eugene C. Murdock: Ban Johnson: Czar of Baseball, Contributions to the Study of Popular Culture, Greenwood Press; annotated edition, 1982.
- John T. Pregler: "Tom Loftus: The American League's Forgotten Founding Father", in Baseball Research Journal, SABR, Vol. 49, Nr. 1 (Spring 2020), pp. 26-36.
- Warren N. Wilbert: The Arrival of the American League: Ban Johnson and the 1901 Challenge of the National League Monopoly, McFarland, Jefferson, NC, 2007. ISBN 978-0-7864-3013-0
-  An article examining the differences between the American and National Leagues over the decades in The Hardball Times, part 1.
-  An article examining the differences between the American and National Leagues over the decades in The Hardball Times, part 2.
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