Major League Baseball (MLB) is a professional baseball league, the oldest of the four major professional sports leagues in the United States and Canada. A total of 30 teams play in the National League (NL) and American League (AL), 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.