Claim: Giancarlo Stanton is in a league.

Major League Baseball -LRB- MLB -RRB- is a professional baseball organization , the oldest of the four major professional sports leagues in the United States and Canada . A total of 30 teams now play in the National League -LRB- NL -RRB- and American League -LRB- AL -RRB- , with 15 teams in each league . The NL and AL operated as separate legal entities from 1876 and 1901 respectively . After cooperating but remaining legally separate entities since 1903 , the leagues merged into a single organization led by the Commissioner of Baseball in 2000 . The organization also oversees Minor League Baseball , which comprises about 240 teams affiliated with the Major League clubs . With the World Baseball Softball Confederation , MLB manages the international World Baseball Classic tournament .   Baseball 's first professional team was founded in Cincinnati in 1869 , 30 years after Abner Doubleday supposedly invented the game of baseball . The first few decades of professional baseball were characterized by rivalries between leagues and by players who often jumped from one team or league to another .  The period before 1920 in baseball was known as the dead-ball era ; players rarely hit home runs during this time . Baseball survived a conspiracy to fix the 1919 World Series , which came to be known as the Black Sox Scandal . The sport rose in popularity in the 1920s , and survived potential downturns during the Great Depression and World War II . Shortly after the war , baseball 's color barrier was broken by Jackie Robinson .   The 1950s and 1960s were a time of expansion for the AL and NL , then new stadiums and artificial turf surfaces began to change the game in the 1970s and 1980s . Home runs dominated the game during the 1990s , and media reports began to discuss the use of anabolic steroids among Major League players in the mid-2000s . In 2006 , an investigation produced the Mitchell Report , which implicated many players in the use of performance-enhancing substances , including at least one player from each team .   Today , MLB is composed of thirty teams : twenty-nine in the United States and one in Canada . Teams play 162 games each season and five teams in each league advance to a four-round postseason tournament that culminates in the World Series , a best-of-seven championship series between the two league champions that dates to 1903 . Baseball broadcasts are aired on television , radio , and the Internet throughout North America and in several other countries throughout the world . MLB has the highest season attendance of any sports league in the world with more than 73 million spectators in 2015 .