[7] Formed in 1876 and 1901, respectively, the NL and AL cemented their cooperation with the National Agreement in 1903, making MLB the oldest major professional sports league in the world.

[22] These practices were essentially ended by the National Agreement of 1903, in which AL and NL agreed to respect each other's player contracts, including the contentious reserve clause.

MLB rose in popularity in the decade following the Black Sox Scandal, and unlike major leagues in other sports, it endured the Great Depression and World War II without any of its teams folding.

[32] The modern Chicago Cubs and Atlanta Braves franchises trace their histories back to the National Association of Professional Base Ball Players in the 1870s.

[23] Games of this era tended to be low-scoring and were often dominated by pitchers, such as Walter Johnson, Cy Young, Christy Mathewson, Mordecai Brown, and Grover Cleveland Alexander.

Additionally, many ballparks had large dimensions, such as the West Side Grounds of the Chicago Cubs, which was 560 feet (170 m) to the center field fence, and the Huntington Avenue Grounds of the Boston Red Sox, which was 635 feet (194 m) to the center field fence, thus home runs were rare, and "small ball" tactics such as singles, bunts, stolen bases, and the hit-and-run play dominated the strategies of the time.

Eight players—"Shoeless" Joe Jackson, Eddie Cicotte, Claude "Lefty" Williams, George "Buck" Weaver, Arnold "Chick" Gandil, Fred McMullin, Charles "Swede" Risberg, and Oscar "Happy" Felsch—intentionally lost the World Series in exchange for a ring worth $100,000 ($1,743,674.03 in 2024 dollars).

[54] Both leagues quickly began to require the use of new, white baseballs whenever a ball became scuffed or dirty, helping bring the "dead-ball" era to an end.

[58] The onset of World War II created a shortage of professional baseball players, as more than 500 men left MLB teams to serve in the military.

MLB teams of this time largely consisted of young men, older players, and those with a military classification of 4F, indicating mental, physical, or moral unsuitability for service.

[60] On January 14, 1942, MLB commissioner Kenesaw Mountain Landis wrote to U.S. president Franklin D. Roosevelt, pleading for the continuation of baseball during the war.

The war interrupted the careers of stars including Stan Musial, Bob Feller, Ted Williams, and Joe DiMaggio, but baseball clubs continued to field their teams.

In what was later referred to as "The Noble Experiment", Robinson was the first black baseball player in the International League since the 1880s, joining the Dodgers' farm club, the Montreal Royals, for the 1946 season.

Robinson received significant encouragement from several major-league players, including Dodgers teammate Pee Wee Reese who said, "You can hate a man for many reasons.

Satchel Paige was signed by the Indians and the Dodgers added star catcher Roy Campanella and Don Newcombe, who was later the first winner of the Cy Young Award for his outstanding pitching.

Giants owner Horace Stoneham had been contemplating a move to Minnesota amid slumping attendance at the aging Polo Grounds ballpark[72] when O'Malley invited him to meet San Francisco mayor George Christopher in New York.

Plans for MLB contraction were halted when the Twins landlord was awarded a court injunction that required the team to play its 2002 home games at their stadium.

In recent years, with the advent of technologies such as Statcast and its use of Hawk-Eye starting in 2020[93] as well as with advanced statistics as provided by sites such as FanGraphs and Baseball Savant, MLB has evolved.

[95] In 2019, Major League Baseball opened an investigation into allegations that members of the 2017 World Series champion Houston Astros stole signs from opposing teams using technology during the 2017 and 2018 seasons.

[104] Under the direction of the commissioner of baseball, MLB hires and maintains the sport's umpiring crews, and negotiates marketing, labor, and television contracts.

[123] The New York Knickerbockers were the first baseball team to use uniforms, taking the field on April 4, 1849, in pants made of blue wool, white flannel shirts (jerseys) and straw hats.

[141] In early-to-mid July, just after the midway point of the season, the Major League Baseball All-Star Game is held during a four-day break from the regular-season schedule.

[143] The fan voting was discontinued after a 1957 ballot-box-stuffing scandal in Cincinnati: seven of the eight slots originally went to Reds players, two of whom were subsequently removed from the lineup to make room for Willie Mays and Hank Aaron.

[158] In October 2013, Phil Rogers of the Chicago Tribune wrote that MLB was considering postseason all-star tours in Taiwan and Korea; baseball is increasing in popularity in both countries.

[162] The San Diego Padres and Los Angeles Dodgers opened the 2024 regular season on March 20–21 at Gocheok Sky Dome in Seoul, South Korea.

The ceremonial first pitch of the opening game was thrown by the first Korean-born MLB player Chan Ho Park, who made his debut with the LA Dodgers in 1994.

[164] In 1998, both Mark McGwire and Sammy Sosa hit more home runs than the record of 61 set by Yankees right fielder Roger Maris in 1961.

[176] Mitchell acknowledged that his "tight relationship with Major League Baseball left him open to criticism",[177] but he said that readers who examine the report closely "will not find any evidence of bias, of special treatment of the Red Sox".

[179] In 2009, allegations surfaced against Alex Rodriguez and David Ortiz, and Manny Ramirez received a 50-game suspension after testing positive for banned substances.

[226] Both Canadian teams (the Montreal Expos before their move to Washington, DC in 2005, and the Toronto Blue Jays) have produced radio broadcasts in French.