From 1942 to 1967, the league had only six teams, collectively (if not contemporaneously) nicknamed the "Original Six".
The NHL replaced the NHA as one of the leagues that competed for the Stanley Cup, which was an interleague competition back then.
Toronto won the first NHL title, and then defeated the Vancouver Millionaires of the Pacific Coast Hockey Association (PCHA) for the 1918 Stanley Cup.
Founded in 1909, the NHA began play one year later with seven teams in Ontario and Quebec, and was one of the first major leagues in professional ice hockey.
But by the NHA's eighth season, a series of disputes with Toronto Blueshirts owner Eddie Livingstone led the other team owners, representing the Montreal Canadiens, Montreal Wanderers, Ottawa Senators, and Quebec Bulldogs to meet about the league's future.
The league then increased to 18 teams in 1974 and 21 teams in 1979.
In the 1990s, the NHL further expanded to 30 teams, and added its 31st team in 2017.The league's headquarters have been in New York City since 1989 when the head office moved there from Montreal.After a labour-management dispute that led to the cancellation of the entire 2004–05 season, the league resumed play in 2005–06 under a new collective agreement that included a salary cap.A new collective bargaining agreement was eventually ratified in July 2005, including a salary cap.The agreement had a term of six years with an option of extending the collective bargaining agreement for an additional year at the end of the term, allowing the league to resume as of the 2005–06 season.Realizing the NHA constitution left them unable to force Livingstone out, the four teams voted instead to suspend the NHA, and on November 26, 1917, formed the National Hockey League.