The Beginning
In 1907 the National Hockey League was formed. Before the original six era began from 1907 to 1941 there were 16 teams that had existed at some point in that time period. Between 1907 and 1926 there were six hockey teams that would become mainstays in the NHL these teams were the Toronto Maple Leafs, Montreal Canadiens, Boston Bruins, New York Rangers, Chicago BlackHawks, and the Detroit Redwings. So they aren't all the original six hockey teams but more like the final six left standing.
Canada's Dominace
In the 25 year span of the original six era, two teams Toronto Maple Leafs and the Montreal Canadiens won a combined 19 of the 25 Stanley Cups. Only two of the four American teams (Chicago BlackHawks 1 and Detroit Red Wings 5) won Stanley Cups in this span. The Canadian teams were so dominant in this span because the Canadiens managed to pull off some of the most lopsided trades in history. Also, teams were granted territorial rights over players and French Canadians usually were the best prospects. The Maple Leafs were able to have gritty playoff games against opponents with having territorial rights over very good players which helped them net 9 Stanley Cup wins in the Original Six era. In 1969 there was a rule implemented for the NHL draft that allowed all amateurs under the age of 20 to become eligible to be drafted by any team. No longer being allowed to hold on to their territorial talent this saw the demise of the Maple Leafs Dominance in the final years of the Original Six era.
End of An Era
In 1967 there was an expansion draft to add six new teams to the NHL. These new teams were located in Los Angeles, Oakland, St. Louis, Minnesota, Pittsburgh, and Philadelphia. This was the first time ever that a sports team double in size from one expansion. In this time this gave aging players a chance to continue their careers and gave many others a chance to play in the NHL. After over 50 years 4 of those six teams in Los Angeles, Pittsburgh, Philadelphia, and St. Louis (the NHL did return to Minnesota in 2000).