Which game variation existed first, and when and why was the second variation developed?
As a very brief history:
- 1845: the first rules of "rugby football" are written down.
- 1871: The Rugby Football Union (RFU) is formed. This is the same body as today's RFU which governs rugby union in England.
- (1880: as well as the union vs league split, 1880 is when the American versions of the game moved from contested scrummages to an uncontested line of scrimmage, thus leading to American and Canadian football today).
- 1895: The Northern Rugby Football Union (NRFU) splits from the Rugby Football Union. The split is not over the rules of the game per se, but over professionalism with the RFU maintaining an strictly amateur stance and the NRFU allowing payments to players. The NRFU is the same body as today's Rugby Football League which governs professional rugby league in England.
- 1995: (yes, 100 years later) The International Rugby Board, the governing body for international rugby union, removes the amateur restrictions on the game. Both codes are now fully professional.
Source: mostly Rugby football on Wikipedia.