The National Basketball Association, often abbreviated to the NBA, is the pre-eminent men's professional basketball league in North America which composes thirty franchised member clubs, of which twenty-nine are located in the United States and one in Canada. It is an active member of USA Basketball (USAB), which is recognized by the International Basketball Federation as the National Governing Body (NGB) for basketball in the United States. The NBA is one of the four major North American professional sports leagues, which include Major League Baseball (MLB), the National Football League (NFL), and the National Hockey League (NHL).
The league was founded in New York City on June 6, 1946 as the Basketball Association of America (BAA). The league adopted the name National Basketball Association in 1949 after merging with the rival National Basketball League (NBL). The league's several international as well as individual team offices are directed out of its head offices located in the Olympic Tower at 645 Fifth Avenue in New York City. NBA Entertainment and NBA TV studios are directed out of offices located in Secaucus, New Jersey.
The Basketball Association of America was founded in 1946 by the owners of the major ice hockey arenas in the Northeastern and Midwestern United States and Canada. On November 1, 1946, in Toronto, Ontario, Canada, the Toronto Huskies hosted the New York Knickerbockers at Maple Leaf Gardens, which the NBA now regards as the first game played in the league's history. Although there had been earlier attempts at professional basketball leagues, including the American Basketball League and the NBL, the BAA was the first league to attempt to play primarily in large arenas in major cities. During its early years, the quality of play in the BAA was not significantly better than in competing leagues or among leading independent clubs such as the Harlem Globetrotters. For instance, the 1948 ABL finalist Baltimore Bullets moved to the BAA and won that league's 1948 title, and the 1948 NBL champion Minneapolis Lakers won the 1949 BAA title.
 1950s: The early years
On August 3, 1949, the BAA agreed to merge with the NBL, creating the new National Basketball Association. The new league had seventeen franchises located in a mix of large and small cities, as well as large arenas and smaller gymnasiums and armories. In 1950, the NBA consolidated to eleven franchises, a process that continued until 1953-54, when the league reached its smallest size of eight franchises, all of which are still in the league (the Knicks, Celtics, Warriors, Lakers, Royals/Kings, Pistons, Hawks, and Nationals/76ers).
The process of contraction saw the league's smaller-city franchises move to larger cities. The Hawks shifted from "Tri-Cities" (the area now known as the Quad Cities) to Milwaukee (in 1951) and then to St. Louis (in 1955); the Royals from Rochester to Cincinnati (in 1957); and the Pistons from Fort Wayne to Detroit (in 1957). In 1960, the Lakers relocated to Los Angeles, and the Warriors moved to San Francisco in 1963. The following year, the Nationals left Syracuse to bring basketball back to Philadelphia, changing their nickname from "Nationals" to "76ers." Thus far, out of the original eight franchises, only the Knicks and Celtics have not relocated.
Although Japanese-American Wataru Misaka technically broke the NBA color barrier in the 1947–48 season when he played for the New York Knicks, 1950 is recognized as the year the NBA integrated. This year witnessed the addition of African American players by several teams, including Chuck Cooper with the Boston Celtics, Nat "Sweetwater" Clifton with the New York Knicks, and Earl Lloyd with the Washington Capitols.
During this period, the Minneapolis Lakers, led by center George Mikan, won five NBA Championships and established themselves as the league's first dynasty. To encourage shooting and discourage stalling, the league introduced the 24-second shot clock in 1954. If a team does not attempt to score a field goal (or the ball fails to make contact with the rim) within 24 seconds of obtaining the ball, play is stopped and the ball given to its opponent.
In 1957, rookie center Bill Russell joined the Boston Celtics, who already featured guard Bob Cousy and coach Red Auerbach, and went on to lead the club to eleven NBA titles in thirteen seasons. Center Wilt Chamberlain entered the league with the Warriors in 1959 and became a dominant individual star of the 1960s, setting new single game records in scoring (100) and rebounding (55). Russell's rivalry with Chamberlain became one of the great individual rivalries in the history of American team sports