The Founding of the National League

February 2, 1876:

 The National League of Professional Baseball Clubs of Major League Baseball is formed. By 1875, the National Association of Professional Base Ball Players was dangerously weak. The N.A. suffered from a lack of strong authority over clubs, unsupervised scheduling, unstable membership, dominance by one team (the Boston Red Stockings), and an extremely low entry fee ($10; $172 in 2007 dollars, adjusted for inflation) that gave clubs no incentive to abide by league rules when it was not convenient.
William Hulbert, a Chicago businessman and an officer of the Chicago White Stockings, approached several N.A. clubs with the plans for a league with stronger central authority and exclusive territories in larger cities only. Additionally, Hulbert had a problem — five of his star players were threatened with expulsion from the NAPBBP because Hulbert had signed them to his club using what were considered questionable means. Hulbert had a great vested interest in creating his own league. After recruiting St. Louis privately, four western clubs met in Louisville, Kentucky, in January 1876. With Hulbert speaking for the four in New York City on February 2, 1876, the National League was established with eight charter members, as follows:

• Chicago White Stockings from the N.A. (now the Chicago Cubs)
• Philadelphia Athletics from the N.A. (expelled after the 1876 season)
• Boston Red Stockings, the dominant team in the N.A. (now the Atlanta Braves, not to be confused with the present-day Boston Red Sox of the American League)
• Hartford Dark Blues from the N.A. (folded after the 1877 season)
• Mutual of New York from the N.A. (expelled after the 1876 season)
• St. Louis Brown Stockings from the N.A. (folded after the 1877 season, having committed to Louisville stars for 1878)
• Cincinnati Red Stockings a new franchise (expelled after the 1880 season)
• Louisville Grays, a new franchise (folded after the 1877 season when four players were banned for gambling)

The National League's formation meant the end of the N.A., as its remaining clubs shut down or reverted to amateur or minor status. The only strong club from 1875 excluded in 1876 was a second one in Philadelphia, often called the White Stockings or Phillies.

Only the Cubs and the Braves have had a continuous existence in the league.  I'll elaborate on the Reds getting the boot some other time.