List of World Series champions
The World Series is the annual championship series of Major League Baseball (MLB) and concludes the MLB postseason. First played in 1903, the World Series championship is determined through a best-of-seven playoff and is a contest between the champions of baseball's National League (NL) and American League (AL). Often referred to as the "Fall Classic", the modern World Series has been played every year since 1903 with two exceptions: in 1904, when the NL champion New York Giants declined to play the AL champion Boston Americans; and in 1994, when the series was canceled due to the players' strike.
World Series
The number of teams was unchanged until 1961, with fourteen expansion teams joining MLB since then. Twelve have played in a World Series (the Mariners and Expos/Nationals being the two exceptions). The expansion teams have won ten of the 22 Series (45%) in which they have played, which is 9% of all 114 series played since 1903. In 2015, the first World Series featuring only expansion teams was played between the Kansas City Royals and New York Mets.
This information is up to date through the present time:When two teams share the same state or metropolitan area, fans often develop strong loyalties to one and antipathies towards the other, sometimes building on already-existing rivalries between cities or neighborhoods. Before the introduction of interleague play in 1997, the only opportunity for two teams playing in the same area but in different leagues to face each other in official competition would have been in a World Series.