1876: Founding of the National League (NL)

The NL was established with eight teams.

1877

• The New York Mutuals and Philadelphia Athletics were expelled.
• The Hartford Dark Blues moved to Brooklyn and became the Brooklyn Hartfords.

1878

• The Brooklyn Hartfords, Louisville Grays, and St. Louis Brown Stockings folded.
• The Indianapolis Blues, Milwaukee Grays, and Providence Grays joined.

1879

• The Indianapolis Blues and Milwaukee Grays folded.
• The Buffalo Bisons, Cleveland Blues, Syracuse Stars, and Troy Trojans joined.

1880

• The Syracuse Stars folded.
• The Cincinnati Reds disbanded and were replaced by the Cincinnati Stars.
• The Worcester Worcesters joined.

1881

• The Cincinnati Stars were expelled because they refused to sign a league-wide pledge to ban alcohol at ballparks.
• The Detroit Wolverines joined.

1882: Establishment of the American Association (AA)

The AA was established with six teams.

1883

• The Troy Trojans and Worcester Worcesters folded.
• The New York Gothams and Philadelphia Quakers joined the NL.
• The Columbus Buckeyes and New York Metropolitans joined the AA.
• The Boston Red Caps became the Boston Beaneaters.
• The new St. Louis Brown Stockings became the St. Louis Browns.

1884: The Union Association (UA) as a third league

• The UA was established with 8 teams.
• The Brooklyn Atlantics, Indianapolis Hoosiers, Toledo Blue Stockings, and Washington Nationals joined the AA.
• The Altoona Mountain Citys folded early-season and were replaced by the Kansas City Cowboys.
• The Washington Nationals from the AA folded mid-season and were replaced by the Richmond Virginians from Minor League Baseball.
• The Philadelphia Keystones folded mid-season and were replaced by the Wilmington Quicksteps from Minor League Baseball.
• The Chicago Browns moved to Pittsburgh and became the Pittsburgh Stogies.
• The Wilmington Quicksteps and Pittsburgh Stogies folded late-season and were replaced by the Milwaukee Brewers from Minor League Baseball and St. Paul Saints, respectively.

1885: Back to two leagues

• The UA disbanded.
• The St. Louis Maroons from the UA joined the NL.
• The Cleveland Blues, Columbus Buckeyes, Indianapolis Hoosiers, Toledo Blue Stockings, and Washington Nationals folded.
• The Richmond Virginians returned to Minor League Baseball.
• The New York Gothams became the New York Giants.
• The Brooklyn Atlantics became the Brooklyn Grays.
• The Louisville Eclipse became the Louisville Colonels.

1886

• The Buffalo Bisons transferred to Minor League Baseball.
• The Providence Grays folded.
• A new Kansas City Cowboys and Washington Nationals joined the NL.

1887

• The Kansas City Cowboys folded.
• The St. Louis Maroons moved to Indianapolis and became the Indianapolis Hoosiers.
• The Pittsburgh Alleghenys transferred to the NL.
• A new Cleveland Blues joined the AA.

1888

• The Brooklyn Grays became the Brooklyn Bridegrooms.
• The New York Metropolitans folded.
• A new Kansas City Cowboys joined the AA.

1889

• The Detroit Wolverines folded.
• The Cleveland Blues transferred to the NL and became the Cleveland Spiders.
• The Columbus Solons joined the AA.

1890: The Players' League (PL) as a third league

• The PL was established with 8 teams.
• The Chicago White Stockings became the Chicago Colts.
• The Philadelphia Quakers became the Philadelphia Phillies.
• The Brooklyn Bridegrooms transferred to the NL.
• The Cincinnati Red Stockings transferred to the NL and became the Cincinnati Reds.
• The Indianapolis Hoosiers, Kansas City Cowboys, and Washington Nationals folded.
• The Baltimore Orioles transferred to Minor League Baseball and were replaced by the Brooklyn Gladiators. The Brooklyn Gladiators then folded mid-season, and the Baltimore Orioles returned to the AA to finish the season.
• The Rochester Broncos, a new Syracuse Stars, and the Toledo Maumees joined the AA.

1891: Last AA season

• The PL disbanded.
• The Brooklyn Bridegrooms became the Brooklyn Grooms.
• The Pittsburgh Alleghenys became the Pittsburgh Pirates.
• The Boston Reds from the PL joined the AA.
• The new Philadelphia Athletics from the AA were expelled and replaced by the new Philadelphia Athletics from the PL.
• The Cincinnati Kelly's Killers joined the AA. They then folded mid-season and were replaced by the new Milwaukee Brewers from Minor League Baseball.
• The Washington Statesmen joined the AA.

1892: NL monopoly

• The AA folded.
• The Baltimore Orioles, Louisville Colonels, St. Louis Browns, and Washington Statesmen (all from the AA) joined the NL.
• The Washington Statesmen became the Washington Senators.

1896

The Brooklyn Grooms became the Brooklyn Bridegrooms again.

1898

The Chicago Colts became the Chicago Orphans.

1899

• The Brooklyn Bridegrooms became the Brooklyn Superbas.
• The St. Louis Browns became the St. Louis Perfectos.

1900: Classic Eight

• The Baltimore Orioles, Cleveland Spiders, Louisville Colonels, and Washington Senators folded.
• The St. Louis Perfectos became the St. Louis Cardinals.

1901: Founding of the American League (AL)

The AL was established with eight teams.

1902

• The new Milwaukee Brewers moved to St. Louis and became the St. Louis Browns.
• The Cleveland Blues became the Cleveland Bronchos

1903: National Agreement and Founding of Major League Baseball (MLB)

• The National League and American League sign the National Agreement, forming Major League Baseball, cementing their cooperation as two leagues under one banner.
• The new Baltimore Orioles folded.
• The New York Highlanders joined the AL.
• The Cleveland Bronchos became the Cleveland Naps.
• The Chicago Orphans became the Chicago Cubs.

1904

The Chicago White Stockings became the Chicago White Sox.

1907

The Boston Beaneaters became the Boston Doves.

1908

The Boston Americans became the Boston Red Sox.

1911

• The Boston Doves became the Boston Rustlers.
• The Brooklyn Superbas became the Brooklyn Trolley Dodgers.

1912

The Boston Rustlers became the Boston Braves.

1913

• The New York Highlanders became the New York Yankees.
• The Brooklyn Trolley Dodgers became the Brooklyn Dodgers.

1914

• The Federal League (FL) declared itself as a "third major league" with its own eight teams, and competed with the NL and AL.
• The Brooklyn Dodgers became the Brooklyn Robins.

1915

• The Cleveland Naps became the Cleveland Indians.
• The Buffalo Buffeds became the Buffalo Blues.
• The Chicago Federals became the Chicago Whales.
• The new Indianapolis Hoosiers moved to Newark, New Jersey, and became the Newark Peppers.

1916

The FL folded prior to the season.

1920: Establishment of the Negro National League (NNL)

The NNL was established with eight teams, the first black baseball league to be designated a major league.

1921

• The Dayton Marcos departed the NNL as an independent team.
• A new Columbus Buckeyes joined the NNL.
• The Cuban Stars became the Cincinnati Cuban Stars.

1922

• The Chicago Giants and Columbus Buckeyes folded.
• The Cleveland Tate Stars and Pittsburgh Keystones joined the NNL.
• The Cincinnati Cuban Stars became the Cuban Stars again.
• The St. Louis Giants became the St. Louis Stars

1923: Founding of the Eastern Colored League (ECL)

• The ECL was established with six teams.
• The Pittsburgh Keystones folded.
• The Milwaukee Bears joined the NNL.
• The Cleveland Tate Stars departed from the NNL as an independent team and were replaced by the Toledo Tigers. The Toledo Tigers then folded mid-season, and the Cleveland Tate Stars returned to the NNL to finish the season.

1924

• The Milwaukee Bears folded.
• The Birmingham Black Barons and Cleveland Browns joined the NNL.
• The Harrisburg Giants and Washington Potomacs joined the ECL.
• After the Indianapolis ABCs temporarily drop out for the season in June, the Memphis Red Sox replace them

1925

• The Cleveland Browns folded.
• The Indianapolis ABCs resume their tenure in the NNL.
• The Washington Potomacs moved to Wilmington, Delaware and became the Wilmington Potomacs and then folded mid-season.

1926

• The Cleveland Elites joined the NNL and folded mid-season.
• The Dayton Marcos returned to the NNL and departed mid-season as an independent team.
• The Newark Stars joined the ECL and folded mid-season.
• The Birmingham Black Barons and Memphis Red Sox departed the NNL and joined Minor League Baseball's Negro Southern League (NSL).

1927

• The Indianapolis ABCs folded.
• The Birmingham Black Barons and Memphis Red Sox returned to the NNL.
• The Cleveland Hornets joined the NNL.

1928: Last ECL season

• The Cleveland Hornets folded.
• The Brooklyn Royal Giants, Harrisburg Giants and Hilldale Club withdrew from the ECL as independent teams.
• The Cleveland Tigers joined the NNL.
• The Philadelphia Tigers joined the ECL.
• The ECL then disbanded mid-season.

1929: Only American Negro League (ANL) season

• The ANL was established with six teams. Five of those teams were from the ECL. The independent Homestead Grays also joined the ECL.
• The Cleveland Tigers folded.
• The Philadelphia Tigers folded.

1930

• The Atlantic City Bacharach Giants and the Cuban Stars from the ANL folded.
• The Baltimore Black Sox, Hilldale Club, Homestead Grays, and New York Lincoln Giants became independent teams.
• The ANL disbanded.
• The Louisville Black Caps and Nashville Elite Giants joined the NNL.

1931: Last NNL season

• The Cuban Stars folded.
• The Birmingham Black Barons and Memphis Red Sox departed the NNL and joined the NSL.
• The Kansas City Monarchs departed the NNL as an independent team (though remains loosely associated with the league).
• A new Indianapolis ABCs joined the NNL.
• The Chicago American Giants became the Chicago Columbia Giants
• The Louisville Black Caps became the Louisville White Sox
• The Nashville Elite Giants moved to Cleveland, Ohio and became the Cleveland Cubs.
• The NNL disbanded mid-season; although, teams continued to play each other as independent teams.

1932: Major league NSL season and only East–West League (EWL) season

• The Detroit Stars and St. Louis Stars folded.
• The Cleveland Cubs moved back to Nashville, Tennessee and became the Nashville Elite Giants again.
• The EWL was established with eight teams. Three of those teams, the Baltimore Black Sox, Hilldale Club, and Homestead Grays were from the ANL.
• The NSL was considered a major league for the season with 10 teams. Five of those teams, the Birmingham Black Barons, Chicago Columbia Giants, Indianapolis ABCs, Memphis Red Sox, and Nashville Elite Giants were from the NNL.
• The Brooklyn Robins became the Brooklyn Dodgers again.
• The Chicago Columbia Giants became the Chicago American Giants again.
• The Newark Browns departed mid-season as an independent team.

1933: Establishment of the second NNL

• The Little Rock Grays and Columbus Turf Club folded.
• The Atlanta Black Crackers and Birmingham Black Barons withdrew as independent teams.
• The NSL was demoted to minor league status.
• The Cleveland Stars, Detroit Wolves, Hilldale Club, and Newark Browns folded.
• Pollock's Cuban Stars and the Washington Pilots withdrew as independent teams.
• The Baltimore Black Sox became the Baltimore Sox.
• The EWL disbanded.
• The second NNL was established with 7 teams. Five of those teams, the Baltimore Sox, Chicago American Giants, Homestead Grays, Indianapolis ABCs, and Nashville Elite Giants were from the NSL or EWL.
• The Pittsburgh Crawfords joined the NNL.
• The Indianapolis ABCs moved mid-season to Detroit, Michigan and became the Detroit Stars.
• The Columbus Blue Birds joined the NNL. The team disbanded and merged with the independent Akron Black Tyrites after the first half of the split season. The Akron Black Tyrites joined the NNL in place of the Columbus Blue Birds before they shortly moved to Cleveland, Ohio and became the Cleveland Giants.

1934

• The Cleveland Giants and Detroit Stars folded.
• The Homestead Grays withdrew as an independent team.
• The Cleveland Red Sox, Newark Dodgers, Philadelphia Bacharach Giants, and Philadelphia Stars joined the NNL.
• The Baltimore Sox became the Baltimore Black Sox again.

1935

• The Cleveland Red Sox folded.
• The Baltimore Black Sox and Philadelphia Bacharach Giants withdrew as independent teams.
• The Brooklyn Eagles and New York Cubans joined the NNL and the Homestead Grays returned to the NNL.
• The Nashville Elite Giants moved to Columbus, Ohio and became the Columbus Elite Giants.

1936

• The Chicago American Giants withdrew.
• The Brooklyn Eagles and Newark Dodgers merged and became the Newark Eagles.
• The New York Black Yankees joined the NNL.
• The Columbus Elite Giants moved to Washington, D.C. and became the Washington Elite Giants.
• The Boston Braves became the Boston Bees.

1937: Founding of the Negro American League (NAL)

• The NAL was established with eight teams. Four of those teams, the Birmingham Black Barons, Chicago American Giants, Kansas City Monarchs, and Memphis Red Sox were from the NSL or the first NNL.
• The New York Cubans withdrew.

1938

• The Cincinnati Tigers, the new Detroit Stars, the Indianapolis Athletics, and the new St. Louis Stars folded.
• The Atlanta Black Crackers, a new Indianapolis ABCs, and the Jacksonville Red Caps joined the NAL.
• The Washington Black Senators joined the NNL.
• The Washington Elite Giants moved to Baltimore, Maryland and became the Baltimore Elite Giants.

1939

• The Washington Black Senators folded.
• The Birmingham Black Barons withdrew.
• The New York Cubans returned to the NNL.
• The Indianapolis ABCs moved to St. Louis, Missouri and became the St. Louis Stars.
• The Atlanta Black Crackers moved to Indianapolis, Indiana and became the Indianapolis ABCs.
• The Jacksonville Red Caps moved to Cleveland, Ohio and became the Cleveland Bears.
• The Pittsburgh Crawfords moved to Toledo, Ohio and became the Toledo Crawfords.
• The Toledo Crawfords withdrew and joined the NAL mid-season.

1940

• The Indianapolis ABCs folded.
• The Birmingham Black Barons returned to the NAL.
• The St. Louis Stars split their home games between St. Louis, Missouri and New Orleans, Louisiana and became the St. Louis–New Orleans Stars.
• The Toledo Crawfords moved to Indianapolis, Indiana and became the Indianapolis Crawfords.

1941

• The Indianapolis Crawfords folded.
• The Cleveland Bears moved back to Jacksonville, Florida and became the Jacksonville Red Caps again.
• The Boston Bees became the Boston Braves again.

1942

• The St. Louis–New Orleans Stars disbanded.
• The Cincinnati Buckeyes joined the NAL.
• The Jacksonville Red Caps folded mid-season.
• The Philadelphia Phillies became the Philadelphia Phils

1943

• The St. Louis–New Orleans Stars returned to the NNL as the Harrisburg–St. Louis Stars, since they moved to Harrisburg, Pennsylvania; although, they kept the St. Louis moniker as a part of their name. The team proceeded to withdraw in July to barnstorm, and then they folded.
• The Cincinnati Buckeyes moved to Cleveland, Ohio and became the Cleveland Buckeyes.
• The Cincinnati Clowns joined the NAL.
• The Philadelphia Phils revert to the Philadelphia Phillies.

1944

The Cincinnati Clowns split their home games between Cincinnati, Ohio and Indianapolis, Indiana and became the Cincinnati–Indianapolis Clowns.

1946

The Cincinnati–Indianapolis Clowns stopped playing in Cincinnati, Ohio and permanently played in Indianapolis, Indiana and became the Indianapolis Clowns.

1947

The Brooklyn Dodgers, Cleveland Indians, and St. Louis Browns integrated.

1948

1949

• The New York Black Yankees folded.
• Due to the ongoing process of integration, the NAL loses its major league status, while the NNL folded. All of the NNL teams, except for the newly independent Homestead Grays joined the NAL.
• The New York Giants integrated.

1950

The Boston Braves integrated.

1951

The Chicago White Sox integrated.

1953: Braves relocation to Milwaukee, and Cincinnati renaming

• The Boston Braves moved to Milwaukee and became the Milwaukee Braves.
• The Cincinnati Reds became the Cincinnati Redlegs.
• The Chicago Cubs, Philadelphia Athletics, and Pittsburgh Pirates integrated.

1954: Browns relocation to Baltimore

• The St. Louis Browns moved to Baltimore and became the Baltimore Orioles.
• The Cincinnati Redlegs, St. Louis Cardinals, and Washington Senators integrated.

1955: Athletics relocation to Kansas City

• The Philadelphia Athletics moved to Kansas City, Missouri, and became the Kansas City Athletics.
• The New York Yankees integrated.

1957

The Philadelphia Phillies integrated.

1958: The NL exits New York for California

• The Brooklyn Dodgers moved to Los Angeles and became the Los Angeles Dodgers.
• The New York Giants moved to San Francisco and became the San Francisco Giants.
• The Detroit Tigers integrated.

1959: Cincinnati reverts back to the Reds

• The Cincinnati Redlegs became the Cincinnati Reds again.
• The Boston Red Sox integrated.

1961 relocation and expansion

• The Washington Senators moved to the Minneapolis–Saint Paul area and became the Minnesota Twins.
• The Los Angeles Angels and a new Washington Senators joined the AL.

1962 expansion

• The Houston Colt .45s and New York Mets joined the NL.

1965: Houston and Angels renaming

• The Houston Colt .45s became the Houston Astros.
• The Los Angeles Angels became the California Angels on September 2, 1965, with 28 games left in the season.

1966: Braves relocation to Atlanta

The Milwaukee Braves moved to Atlanta and became the Atlanta Braves.

1968: Athletics relocation to Oakland

The Kansas City Athletics moved to Oakland, California, and became the Oakland Athletics.

1969 expansion and realignment

• The Kansas City Royals and Seattle Pilots joined the AL.
• The Montreal Expos and San Diego Padres joined the NL.
• The two leagues each realigned into two six-team divisions

1970: Pilots relocation to Milwaukee

The Seattle Pilots moved to Milwaukee and became the Milwaukee Brewers.

1972: Senators relocation to the Dallas–Fort Worth metroplex

• The Washington Senators moved to Arlington, Texas, in the Dallas–Fort Worth metroplex and became the Texas Rangers.
• The Texas Rangers and Milwaukee Brewers switched divisions.

1977 expansion

• The Seattle Mariners joined the AL West.
• The Toronto Blue Jays joined the AL East.

1993 expansion

• The Colorado Rockies joined the NL West.
• The Florida Marlins joined the NL East.

1994 realignment

MLB realigned to three divisions in each league to accommodate an expanded postseason format with a wild card team (although this new playoff format would not be fully implemented until 1995 due to a work stoppage):

• The AL Central was formed with the Cleveland Indians and Milwaukee Brewers transferring from the AL East, and the Chicago White Sox, Kansas City Royals, and Minnesota Twins transferred from the AL West.
• The NL Central was formed with the Chicago Cubs, Pittsburgh Pirates, and St. Louis Cardinals transferring from the NL East, and the Cincinnati Reds and Houston Astros transferred from the NL West.
• The Atlanta Braves transferred to the NL East.

1997: Angels renaming

The California Angels became the Anaheim Angels.

1998 expansion

• The Arizona Diamondbacks joined the NL West.
• The Tampa Bay Devil Rays joined the AL East.
• The Detroit Tigers transferred to the AL Central.
• In order to primarily continue intraleague play, the Milwaukee Brewers transferred to the NL Central so both leagues would have an even number of teams.

2005: Expos relocation and Angels renaming

• The Montreal Expos moved to Washington, D.C. and became the Washington Nationals.
• The Anaheim Angels became the Los Angeles Angels of Anaheim.

2008: Tampa Bay renaming

The Tampa Bay Devil Rays became the Tampa Bay Rays.

2012: Marlins renaming

The Florida Marlins became the Miami Marlins.

2013: Astros switch leagues

With interleague play expanded to occur throughout the season, the Houston Astros transferred to the AL West to accommodate each league with 15 clubs apiece.

2016: Angels renaming

The Los Angeles Angels of Anaheim became the Los Angeles Angels.

2022: Cleveland renaming

The Cleveland Indians became the Cleveland Guardians.