The National Hockey Association was formed in 1910 with its membership being all Canadian, the Montreal Shamrocks, the Montreal Wanderers, the Renfrew Millionaires and also teams from Cobalt, and Haileybury, unlikely now a site to be on the radar for NHL expansion.
When the NHL came into existence in 1917, there were 4 teams established. They were all Canadian – The Montreal Canadiens, the Montreal Wanderers, the Ottawa Senators and the Toronto Arenas. (what a creative name! )The actual name was the Arena Hockey Club of Toronto.
As a completely unrelated aside, this Toronto team was mired in litigation with the prior owner of the Toronto team from the N.H.A. It ceased operation at the end of the 1918-1919 season. The Toronto St. Patricks emerged in the 1919-1920 season. This team later became the Leafs.
The Wanderers home rink burned down on January 2, 1918. The Canadiens team shared the same arena and then moved in the Jubilee rink. The Wanderers folded. The league continued with just three teams.
The Quebec Bulldogs was intended as an active team but did not participate until 1919. All but the Toronto team had been members of the NHA.
Somehow I suppose it seemed natural enough to let these guys have a shot at it. After all, prior to the agreement with the PCHA, all teams were Canadian and who would then think Gary Bettman would ever be seen some 100 odd years later, in Washington DC of all places ( we just finished burning the sucker in the War of 1812 a few years earlier…Ok…. a hundred or so years earlier ) giving the Dominion Hockey Challenge Cup yet, in front of a bunch of screaming foreigners, who really should have thanked us for letting them rebuild their House White. ( it was red, of course, before we burned it)
The Torontos became the NHL champions in the inaugural year by playing a two game total goals series against the Canadiens by a total score of 10-7. Interestingly the Toronto team then successfully played the winner of the Pacific Coast Hockey Association, the Vancouver Millionaires in a five game series to acquire the Stanley Cup. The year prior the Cup was won by the Seattle Metropolitans, also of the PCHA.
In the following 1918-1919 season the Montreal Canadiens played the same Seattle team. The series was terminated after five games after many players fell ill due to the Spanish influenza. One of the Montreal Canadien players, Joe Hall, died a few weeks following. The Cup was not awarded that year.
An agreement was then in place between the NHA and the PCHA which allowed the respective winners of each league to play one another for the Stanley Cup.
The Western Canada Hockey League was then formed in 1922. The three leagues then competed for the Cup. This format continued for three years after which the PCHA and the WCHL merged to create the Western Hockey League in 1924. The Victoria Cougars became the last non-NHL team to win the trophy.
The WHL disbanded in 1926. After that event, all Stanley Cup winners came from the NHL.