MLB

In the 1860s, aided by soldiers playing the game in camp during the Civil War, "New York"-style baseball expanded into a national game and spawned baseball's first governing body, the National Association of Base Ball Players (NABBP). The NABBP existed as an amateur league for 12 years. By 1867, more than 400 clubs were members. Most of the strongest clubs remained those based in the Northeastern United States. For professional baseball's founding year, MLB uses the year 1869—when the first professional team, the Cincinnati Red Stockings, was established.

A schism developed between professional and amateur ballplayers after the founding of the Cincinnati club. The NABBP split into an amateur organization and a professional organization. The National Association of Professional Base Ball Players, often known as the National Association (NA), was formed in 1871. Its amateur counterpart disappeared after only a few years. The modern Chicago Cubs and Atlanta Braves franchises trace their histories back to the National Association of Professional Base Ball Players in the 1870s.

In 1876, the National League of Professional Base Ball Clubs (later known as the National League or NL) was established after the NA proved ineffective. The league placed its emphasis on clubs rather than on players. Clubs could now enforce player contracts, preventing players from jumping to higher-paying clubs. Clubs were required to play the full schedule of games instead of forfeiting scheduled games when the club was no longer in the running for the league championship, which happened frequently under the NA. A concerted effort was made to curb gambling on games, which was leaving the validity of results in doubt. The first game in the NL—on Saturday, April 22, 1876 (at Jefferson Street Grounds in Philadelphia)—is often pointed to as the beginning of MLB.

The early years of the NL were tumultuous, with threats from rival leagues and a rebellion by players against the hated "reserve clause", which restricted the free movement of players between clubs. Teams came and went; 1882 was the first season where the league's membership was the same as the preceding season's, and only four franchises survived to see 1900. Competitor leagues formed regularly and also disbanded regularly. The most successful was the American Association (1882–1891), sometimes called the "beer and whiskey league" for its tolerance of the sale of alcoholic beverages to spectators. For several years, the NL and American Association champions met in a postseason championship series—the first attempt at a World Series. The two leagues merged in 1892 as a single 12-team NL, but the NL dropped four teams after the 1899 season. This led to the formation of the American League in 1901 under AL president Ban Johnson, and the resulting bidding war for players led to widespread contract-breaking and legal disputes.

The war between the AL and NL caused shock waves throughout the baseball world. At a meeting at the Leland Hotel in Chicago in 1901, the other baseball leagues negotiated a plan to maintain their independence. A new National Association was formed to oversee these minor leagues.

After 1902, the NL, AL, and NA signed a new National Agreement which tied independent contracts to the reserve-clause contracts. The agreement also set up a formal classification system for minor leagues, the forerunner of today's system that was refined by Branch Rickey.

Several other early defunct baseball leagues are considered major leagues, and their statistics and records are included with those of the two modern major leagues. In 1969, the Special Baseball Records Committee of Major League Baseball officially recognized six major leagues: the National League, American League, American Association, Union Association (1884), Players' League (1890), and Federal League (1914–1915). The status of the National Association as a major league has been a point of dispute among baseball researchers; while its statistics are not recognized by Major League Baseball, its statistics are included with those of other major leagues by some baseball reference websites, such as Retrosheet. Some researchers, including Nate Silver, dispute the major-league status of the Union Association by pointing out that franchises came and went and that the St. Louis club was deliberately "stacked"; the St. Louis club was owned by the league's president and it was the only club that was close to major-league caliber.

In December 2020, Major League Baseball announced its recognition of seven leagues within Negro league baseball as major leagues: the first and second Negro National Leagues (1920–1931 and 1933–1948), the Eastern Colored League (1923–1928), the American Negro League (1929), the East–West League (1932), the Negro Southern League (1932), and the Negro American League (1937–1948). In 2021, baseball reference website Baseball-Reference.com began to include statistics from those seven leagues into their major-league statistics. In May 2024, Major League Baseball announced that it was "absorbing the available Negro Leagues numbers into the official historical record."

The period between 1900 and 1919 is commonly referred to as the "dead-ball era". 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. The term also accurately describes the condition of the baseball itself. The baseball used American rather than the modern Australian wool yarn and was not wound as tightly, affecting the distance that it would travel. More significantly, balls were kept in play until they were mangled, soft and sometimes lopsided. During this era, a baseball cost three dollars, equal to $52.72 today (in inflation-adjusted USD), and owners were reluctant to purchase new balls. Fans were expected to throw back fouls and (rare) home runs. Baseballs also became stained with tobacco juice, grass, and mud, and sometimes the juice of licorice, which some players would chew for the purpose of discoloring the ball.

Also, pitchers could manipulate the ball through the use of the spitball (In 1921, use of this pitch was restricted to a few pitchers with a grandfather clause). 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. Hitting methods like the Baltimore chop were used to increase the number of infield singles. On a successful Baltimore chop, the batter hits the ball forcefully into the ground, causing it to bounce so high that the batter reaches first base before the ball can be fielded and thrown to the first baseman.

The adoption of the foul strike rule—in the NL in 1901, in the AL two years later—quickly sent baseball from a high-scoring game to one where scoring runs became a struggle. Before this rule, foul balls were not counted as strikes: a batter could foul off any number of pitches with no strikes counted against him; this gave an enormous advantage to the batter.

After the 1919 World Series between the Chicago White Sox and Cincinnati Reds, baseball was rocked by allegations of a game-fixing scheme known as the Black Sox Scandal. 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 ($1,712,780.35 in 2022 dollars). Despite being acquitted, all were permanently banned from Major League Baseball.

Baseball's popularity increased in the 1920s and 1930s. The 1920 season was notable for the death of Ray Chapman of the Cleveland Indians. Chapman, who was struck in the head by a pitch and died a few hours later, became the only MLB player to die of an on-field injury. 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.

The following year, the New York Yankees made their first World Series appearance. By the end of the 1930s, the team had appeared in 11 World Series, winning eight of them. Yankees slugger Babe Ruth had set the single-season home run record in 1927, hitting 60 home runs; breaking his own record of 29 home runs.

Afflicted by the Great Depression, baseball's popularity had begun a downward turn in the early 1930s. By 1932, only two MLB teams turned a profit. Attendance had fallen, due at least in part to a 10% federal amusement tax added to baseball ticket prices. Baseball owners cut their rosters from 25 men to 23, and even the best players took pay cuts. Team executives were innovative in their attempts to survive, creating night games, broadcasting games live by radio, and rolling out promotions such as free admission for women. Throughout the Great Depression, no MLB teams moved or folded.

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. Many of them played on service baseball teams that entertained military personnel in the US or in the Pacific. 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. Men like Pete Gray, a one-armed outfielder, got the chance to advance to the major leagues. However, MLB rosters did not include any black players through the end of the war. Black players, many of whom served in the war, were still restricted to playing Negro league baseball.

Wartime blackout restrictions, designed to keep outdoor lighting at low levels, caused another problem for baseball. These rules limited traveling and night games to the point that the 1942 season was nearly canceled. 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. Roosevelt responded, "I honestly feel that it would be best for the country to keep baseball going. There will be fewer people unemployed and everybody will work longer hours and harder than ever before. And that means that they ought to have a chance for recreation and for taking their minds off their work even more than before."

With the approval of President Roosevelt, spring training began in 1942 with few repercussions. 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.

Branch Rickey, president and general manager of the Brooklyn Dodgers, began making efforts to introduce a black baseball player to the previously all-white professional baseball leagues in the mid-1940s. He selected Jackie Robinson from a list of promising Negro league players. After obtaining a commitment from Robinson to "turn the other cheek" to any racial antagonism directed at him, Rickey agreed to sign him to a contract for $600 a month. 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.

The following year, the Dodgers called up Robinson to the major leagues. On April 15, 1947, Robinson made his major league debut at Ebbets Field before a crowd of 26,623 spectators, including more than 14,000 black patrons. Black baseball fans began flocking to see the Dodgers when they came to town, abandoning the Negro league teams that they had followed exclusively. Robinson's promotion met a generally positive, although mixed, reception among newspaper writers and white major league players. Manager Leo Durocher informed his team, "I don't care if he is yellow or black or has stripes like a fucking zebra. I'm his manager and I say he plays."

After a strike threat by some players, NL President Ford C. Frick and Baseball Commissioner Happy Chandler let it be known that any striking players would be suspended. 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. Color is not one of them." That year, Robinson won the inaugural Major League Baseball Rookie of the Year Award (separate NL and AL Rookie of the Year honors were not awarded until 1949).

Less than three months later, Larry Doby became the first African-American to break the color barrier in the American League with the Cleveland Indians. The next year, a number of other black players entered the major leagues. 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.

MLB banned the signing of women to contracts in 1952, but that ban was lifted in 1992. There have been no female MLB players.

From 1903 to 1952, the major leagues consisted of two eight-team leagues whose 16 teams were located in ten cities, all in the northeastern and midwestern United States: New York City had three teams and Boston, Chicago, Philadelphia, and St. Louis each had two teams. St. Louis was the southernmost and westernmost city with a major league team. The longest possible road trip, from Boston to St. Louis, took about 24 hours by railroad. After a half-century of stability, starting in the 1950s, teams began to move out of cities with multiple teams into cities that had not had them before. From 1953 to 1955, three teams moved to new cities: the Boston Braves became the Milwaukee Braves, the St. Louis Browns became the Baltimore Orioles, and the Philadelphia Athletics became the Kansas City Athletics.

The 1958 Major League Baseball season began to turn Major League Baseball into a nationwide league. Walter O'Malley, owner of the Brooklyn Dodgers and "perhaps the most influential owner of baseball's early expansion era," moved his team to Los Angeles, marking the first major league franchise on the West Coast. O'Malley also helped persuade the rival New York Giants to move west to become the San Francisco Giants. Giants owner Horace Stoneham had been contemplating a move to Minnesota amid slumping attendance at the aging Polo Grounds ballpark when O'Malley invited him to meet San Francisco Mayor George Christopher in New York. After Stoneham was persuaded to move to California, Time magazine put O'Malley on its cover. MLB Commissioner Ford C. Frick had opposed the meeting, but the dual moves proved successful for both franchises—and for MLB. Had the Dodgers moved out west alone, the St. Louis Cardinals—1,600 mi (2,575 km) away—would have been the closest NL team. Instead, the joint move made West Coast road trips economical for visiting teams. The Dodgers set a single-game MLB attendance record in their first home appearance with 78,672 fans.

In 1961, the first Washington Senators franchise moved to Minneapolis–St. Paul to become the Minnesota Twins. Two new teams were added to the American League at the same time: the Los Angeles Angels (who soon moved from downtown L.A. to nearby Anaheim) and a new Washington Senators franchise. The NL added the Houston Astros and the New York Mets in 1962. The Astros (known as the "Colt .45s" during their first three seasons) became the first southern major league franchise since the Louisville Colonels folded in 1899 and the first franchise to be located along the Gulf Coast. The Mets established a reputation for futility by going 40–120 during their first season of play in the nation's media capital—and by playing only a little better in subsequent campaigns—but in their eighth season (1969) the Mets became the first of the 1960s expansion teams to play in the postseason, culminating in a World Series title over the heavily favored Baltimore Orioles.

In 1966, the major leagues moved to the "Deep South" when the Braves moved to Atlanta. In 1968, the Kansas City Athletics moved west to become the Oakland Athletics. In 1969, the American and National Leagues both added two expansion franchises. The American League added the Seattle Pilots (who became the Milwaukee Brewers after one disastrous season in Seattle) and the Kansas City Royals. The NL added the first Canadian franchise, the Montreal Expos, as well as the San Diego Padres.

In 1972, the second Washington Senators moved to the Dallas–Fort Worth metroplex to become the Texas Rangers. In 1977, baseball expanded again, adding a second Canadian team, the Toronto Blue Jays, as well as the Seattle Mariners. Subsequently, no new teams were added until the 1990s and no teams moved until 2005.

By the late 1960s, the balance between pitching and hitting had swung in favor of the pitchers. In 1968—later nicknamed "the year of the pitcher"—Boston Red Sox player Carl Yastrzemski won the American League batting title with an average of just .301, the lowest in the history of Major League Baseball. Detroit Tigers pitcher Denny McLain won 31 games, making him the only pitcher to win 30 games in a season since Dizzy Dean in 1934. St. Louis Cardinals starting pitcher Bob Gibson achieved an equally remarkable feat by allowing an ERA of just 1.12.

Following these pitching performances, in December 1968 the MLB Playing Rules Committee voted to reduce the strike zone from knees to shoulders to top of knees to armpits and lower the pitcher's mound from 15 to 10 inches, beginning in the 1969 season.

In 1973, the American League, which had been suffering from much lower attendance than the National League, sought to increase scoring even further by initiating the designated hitter (DH) rule.

Throughout the 1960s and 1970s, as baseball expanded, NFL football had been surging in popularity, making it economical for many of these cities to build multi-purpose stadiums instead of single-purpose baseball fields. Because of climate and economic issues, many of these facilities had playing surfaces made from artificial turf, as well as the oval designs characteristic of stadiums designed to house both baseball and football. This often resulted in baseball fields with relatively more foul territory than older stadiums. These characteristics changed the nature of professional baseball, putting a higher premium on speed and defense over home-run hitting power since the fields were often too big for teams to expect to hit many home runs and foul balls hit in the air could more easily be caught for outs.

Teams began to be built around pitching—particularly their bullpens—and speed on the basepaths. Artificial surfaces meant balls traveled quicker and bounced higher, so it became easier to hit ground balls "in the hole" between the corner and middle infielders. Starting pitchers were no longer expected to throw complete games; it was enough for a starter to pitch 6–7 innings and turn the game over to the team's closer, a position which grew in importance over these decades. As stolen bases increased, home run totals dropped. After Willie Mays hit 52 home runs in 1965, only one player (George Foster) reached that mark until the 1990s.

During the 1980s, baseball experienced a number of significant changes the game had not seen in years. Home runs were on the decline throughout the decade, with players hitting 40 home runs just 13 times and no one hitting more than 50 home runs in a season for the first time since the Dead-ball era (1900–1919).

The 1981 Major League Baseball strike from June 12 until July 31 forced the cancellation of 713 total games and resulted in a split-season format.

In 1985, Pete Rose broke Ty Cobb's all-time hits record with his 4,192nd hit, and in 1989 Rose received a lifetime ban from baseball as a result of betting on baseball games while manager of the Cincinnati Reds. Rose was the first person to receive a lifetime ban from baseball since 1943. 1985 also saw the Pittsburgh drug trials which involved players who were called to testify before a grand jury in Pittsburgh related to cocaine trafficking.

The 1994–95 Major League Baseball strike from August 12, 1994, to April 25, 1995, caused the cancellation of over 900 games and the forfeit of the entire 1994 postseason.

Routinely in the late 1990s and early 2000s, baseball players hit 40 or 50 home runs in a season, a feat that was considered rare even in the 1980s. It later became apparent that at least some of this power surge was a result of players using steroids and other performance-enhancing drugs.

In 1993, the National League added the Florida Marlins in Miami and the Colorado Rockies in Denver. In 1998, the Brewers switched leagues by joining the National League, and two new teams were added: the National League's Arizona Diamondbacks in Phoenix and the American League's Tampa Bay Devil Rays in Tampa Bay.

After the 2001 season, the team owners voted in favor of contraction. Several MLB teams had been considered for elimination in early talks about contraction, but the Montreal Expos and the Minnesota Twins were the two teams that came closest to folding under the plan. 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. MLB owners agreed to hold off on reducing the league's size until at least 2006.

The Montreal Expos became the first franchise in over three decades to move when they became the Washington Nationals in 2005. This move left Canada with just one team, but it also returned baseball to Washington after a 33-year absence. This franchise shift, like many previous ones, involved baseball's return to a city that had been previously abandoned. Not counting the short-lived Federal League, Montreal is the only city to host an MLB franchise since 1901 that, as of December 2023^[update], does not have a team.

In recent years, with the advent of technologies such as Statcast and its use of Hawk-Eye starting in 2020 as well as with advanced statistics as provided by sites such as FanGraphs and Baseball Savant, MLB has evolved. With the ability to see precise movements of pitchers and batters, teams can assess the mechanics of a player and help them improve. Statcast also provides some features such as tracking the paths of most batted balls, tracking the speed of most batted balls, and tracking the exit velocity of most batted balls. Statcast has allowed for advanced defensive analytics that have not been possible before tracking of players due to how subjective fielding can be.

The rate of teams using a defensive shift has gone up from 13.7% in 2016 to 33.6% in 2022 because advanced statistics support this as an effective way to stop hitters from getting hits. Because the shift reduces the number of balls in play that result in hits and MLB wishes to increase interest in baseball, MLB announced in September 2022 that extreme infield defensive shifts would be banned starting in 2023. In order to be compliant, there must be two fielders on each side of second base, and those fielders must have both of their feet on the infield dirt at the time the pitch is thrown. If this rule is not followed, the choice of an automatic ball or the outcome of the play is given to the batting team.

The game of baseball has also slowed down significantly due to an increased number of strikeouts and walks—two outcomes that generally take many pitches to complete—and an increased amount of time taken for a pitcher to pitch. In 2020, it took an average of three hours and six minutes to complete a 9 inning game, a number which has steadily ticked up for years. Along with the restrictions on defensive shifts, MLB announced the introduction of a pitch clock for the 2023 season and beyond, which is something that has been an experiment in MiLB for a few years. The pitch clock starts at 15 seconds. By the time the clock reaches 10 seconds, the catcher must be in their crouch behind home plate. When the clock reaches 8 seconds, the batter must be in the batter's box and be "alert". Before the 15 second timer reaches 0 seconds, the pitcher must have started their "motion to pitch". If any of these deadlines are violated, the count of the batter will be increased by one ball if the defending team violated the pitch clock or one strike if it is the offensive team who violated the pitch clock. Additionally, in order to prevent circumventing these rules pickoffs and step-offs which reset the pitch clock are only allowed two times total per plate appearance and, if a pitcher attempts a third pickoff and fails to get the runner out, a balk will be called. Similarly, a batter is restricted to calling a timeout (an action which resets the pitch clock) just once per plate appearance.

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. The Astros were found guilty in January 2020 and while no active players faced any repercussions due to an immunity agreement in exchange for testimony, Astros general manager Jeff Luhnow and field manager A. J. Hinch were suspended for the entire 2020 season. The Astros were fined the maximum allowable $5 million and forfeited their first- and second-round picks in the 2020 and 2021 drafts. The Boston Red Sox were also found guilty of stealing signs during the 2017 and 2018 seasons, with the latter season ending in a World Series victory. Red Sox manager Alex Cora was suspended for a year and the team was fined with the loss of a second round draft pick in the 2020 draft as a result.

In November 2023, the Oakland Athletics relocation to Las Vegas was approved by MLB owners.

As of early 2024, MLB has discussed preparations for another round of expansion, and several investment groups are vying for an MLB franchise.