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.

In 2009, the NHL enjoyed record highs in terms of sponsorships, attendance, and television audiences.

Seven years of battling for players and markets financially damaged both leagues, leading to a 1979 merger agreement that saw the WHA cease operations while the NHL absorbed the Winnipeg Jets, Edmonton Oilers, Hartford Whalers and Quebec Nordiques.

The owners initially rejected this merger agreement by one vote, but a massive boycott of Molson Brewery products by fans in Canada caused the Montreal Canadiens, which was owned by Molson, to reverse its position, along with the Vancouver Canucks. Gretzky went on to lead the Oilers to four Stanley Cup championships in 1984, 1985, 19, and set single season records for goals (92 in 1981–82), assists (163 in 1985–86) and points (215 in 1985–86), as well as career records for goals (894), assists (1,963) and points (2,857).

It was the last time a non-NHL team won the trophy, The Great Depression and the onset of World War II took a toll on the league. The league was reduced to six teams for the 1942–43 NHL season: the Boston Bruins, Chicago Black Hawks, Detroit Red Wings, Montreal Canadiens, New York Rangers and Toronto Maple Leafs.

The Pirates became the Philadelphia Quakers in 1930, then folded one year later. These six teams remained constant for 25 years, a period known as the Original Six.

The National Hockey League was established in 1917 as the successor to the National Hockey Association (NHA).

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.

) is a professional ice hockey league currently comprising 31 teams: 24 in the United States and 7 in Canada.

Headquartered in New York City, the NHL is considered to be the premier professional ice hockey league in the world, is awarded annually to the league playoff champion at the end of each season.

At its inception, the NHL had four teams—all in Canada, thus the adjective "National" in the league's name.