Major League Baseball (MLB) is a North American professional baseball organization that was founded in 1903 as a result of the merger of the National League (NL) and the American League (AL).
Since their founding in the nineteenth century, the NL and the AL have operated as separate organizations. In the years leading up to the merger, the two leagues were involved in a "baseball war," with the AL moving its teams into the established NL realm of the East Coast and wooing off some top athletes from NL teams.
In 1903, the leagues reached an agreement that ended up in the establishment of the World Series, which pitted the annual winners of each league against one another to ascertain a national champion, as well as the National Commission, a three-man regulatory council that supervised Major League Baseball until it was supplanted by a single commissioner in 1921.
Major League Baseball's groups are organized as follows:
Atlanta Braves, Miami Marlins, New York Mets, Philadelphia Phillies, and Washington Nationals are the teams in the National League East.
Chicago Cubs, Cincinnati Reds, Milwaukee Brewers, Pittsburgh Pirates, and St. Louis Cardinals are the teams in the National League Central.
NL West: Arizona Diamondbacks, Colorado Rockies, Los Angeles Dodgers, San Diego Padres, San Francisco Giants
Baltimore Orioles, Boston Red Sox, New York Yankees, Tampa Bay Rays, and Toronto Blue Jays are the teams in the American League East.
The Chicago White Sox, Cleveland Indians, Detroit Tigers, Kansas City Royals, and Minnesota Twins are in the AL Central.
Houston Astros, Los Angeles Angels of Anaheim, Oakland Athletics, Seattle Mariners, and Texas Rangers are the teams in the American League West.