Major League Baseball (MLB) has its roots in the mid-19th century, when amateur baseball clubs began to form in cities like New York and Boston. However, it wasn't until 1876 that the first fully professional league was established – the National League of Professional Base Ball Clubs.
The National League consisted of eight teams: the Boston Red Stockings (now Atlanta Braves), Chicago White Stockings (now Chicago Cubs), Cincinnati Red Stockings (now Cincinnati Reds), Hartford Dark Blues, Louisville Grays, New York Mutuals, Philadelphia Athletics, and St. Louis Brown Stockings (now St. Louis Cardinals).
In 1901, the American League of Professional Baseball Clubs was founded by Ban Johnson as a direct competitor to the National League. The American League initially consisted of eight teams: Baltimore Orioles, Boston Americans (now Boston Red Sox), Chicago White Sox, Cleveland Broncos (now Cleveland Guardians), Detroit Tigers, Milwaukee Brewers (moved to St. Paul in 1902 and became the St. Paul Saints), Philadelphia Athletics, and Washington Senators (now Minnesota Twins).