From which defunct professional league did the NHL absorb four teams in 1979?

The NHL absorbed four teams from the World Hockey Association in 1979.

The WHA was founded in 1971 as a rival to the established NHL. It attracted major players, including Bobby Hull and later a young Wayne Gretzky, by offering new teams and competitive salaries. The league struggled with unstable franchises and financial problems, but it pushed the NHL to expand its markets and reconsider player compensation.

When the WHA ceased operations in 1979, four of its clubs entered the NHL for the 1979–80 season: the Edmonton Oilers, New England Whalers, Quebec Nordiques, and Winnipeg Jets. The Whalers were renamed the Hartford Whalers after joining the NHL.

The agreement was formally treated as an expansion rather than a full merger. The NHL did not recognize WHA records, and the incoming teams had to work within roster and draft restrictions. Nevertheless, the former WHA clubs became important NHL franchises: the Oilers won five Stanley Cups in the 1980s, while the Nordiques and Jets later relocated to Colorado and Arizona.