The roots of Major League Baseball trace back to the founding of the National League in 1876, which established the first professional baseball league with a formal structure, schedule, and rules. The American League was founded in 1901 by Ban Johnson, who elevated the minor Western League to major league status and declared it a competitor to the National League.
The two leagues initially competed for players and fans, but in 1903 they signed the National Agreement, establishing a framework for coexistence and creating what would become modern Major League Baseball. The first modern World Series was played in 1903, with the Boston Americans defeating the Pittsburgh Pirates.
The early 20th century established baseball as America's national pastime. Legendary players including Ty Cobb, Honus Wagner, Walter Johnson, and Babe Ruth became national celebrities. The 1919 Black Sox scandal, in which eight Chicago White Sox players were accused of intentionally losing the World Series, led to the establishment of the Commissioner's Office in 1920. Kenesaw Mountain Landis became the first Commissioner and served until 1944.
Babe Ruth's home run hitting transformed the game in the 1920s, and the New York Yankees became the dominant team of the era. The Great Depression challenged baseball economically but the sport endured, and the introduction of night games in 1935 expanded the fan base.
Jackie Robinson broke baseball's color barrier on April 15, 1947, when he debuted for the Brooklyn Dodgers. Robinson's integration of baseball was a landmark moment in American civil rights history, and April 15 is now celebrated as Jackie Robinson Day across MLB.
Television transformed baseball in the 1950s and 1960s, bringing games to national audiences. The league expanded geographically, moving teams from New York to Los Angeles and San Francisco in 1958 and adding expansion teams in subsequent decades. MLB grew from 16 teams in 1960 to 30 teams by 1998.
The free agency era began in 1975 following the Messersmith-McNally arbitration decision, which struck down the reserve clause that had bound players to their teams indefinitely. Free agency dramatically increased player salaries and changed the economics of baseball.
MLB faced significant challenges in the 1990s, including the 1994-95 players' strike that cancelled the World Series for the first time since 1904. The strike damaged fan attendance and trust, but the sport recovered in the late 1990s, partly driven by the home run chase between Mark McGwire and Sammy Sosa in 1998.
The steroid era of the 1990s and 2000s tainted many of baseball's statistical achievements, leading to the Mitchell Report in 2007 and enhanced drug testing programs. Several prominent players, including Barry Bonds, Roger Clemens, and Alex Rodriguez, faced scrutiny over performance-enhancing drug use.
Rob Manfred became Commissioner in January 2015, succeeding Bud Selig. Manfred has implemented significant rule changes aimed at improving the pace of play, including the pitch clock (introduced in 2023), larger bases, and limits on defensive shifts. The 2023 rule changes reduced average game time by approximately 26 minutes, with the 2024 season posting the best average game time (2 hours, 36 minutes) since 1984.
The 2024 World Series was won by the Los Angeles Dodgers, who defeated the New York Yankees. The Dodgers' roster featured Shohei Ohtani, who signed a record 10-year, $700 million contract with the team in December 2023, the largest contract in professional sports history.