Pro hockey once had two leagues, and that couldn't last
Coming Soon - The KHL's North American Division - Mile High Hockey
File:NHLWHAmerger.png - Wikipedia
Today in Non-NHL Hockey History: October 11, 1972: The World
World Hockey Association, sports league
History of the National Hockey League (1967–1992) - Wikipedia
N.H.L. Expansion, From Vegas to Those California Seals - The New
History of the National Hockey League/1967–1992/World Hockey
NHL–WHA merger, NHL Wiki
, details the renegade hockey league formed in 1972 that competed against the established National Hockey league for seven years, before merging
The World Hockey Association Fact Book, Second Edition
The merger that changed the history of the NHL forever
Voices Grow Louder for Merger of Women's Pro Hockey Leagues - The