Major League Baseball is a professional baseball organization. It is the oldest of the major professional sports leagues in the United States and Canada. A total of 30 teams play in Major League Baseball: 15 teams in the National League and 15 in the American League. The NL and AL were formed as separate legal entities in 1876 and 1901, respectively. Beginning in 1903, the two leagues cooperated but remained legally separate entities. In 2000 the leagues merged into a single organization led by the Commissioner of Baseball. MLB also oversees Minor League Baseball, which comprises 256 teams affiliated with the major league clubs. MLB and the World Baseball Softball Confederation jointly manage the international World Baseball Classic tournament. Baseball's first openly all-professional team was the Cincinnati Red Stockings founded in 1869. Before that, some teams had secretly paid some players. 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 is known as the dead-ball era, during which players would rarely hit home runs.