In years leading up to expansion, four of the six NHL teams reached the playoffs. To increase competition, playoff teams were increased to eight. The Original Six made up the East division and the new teams, the West. The four teams from each division would compete in two round action. The winner from the East and West would face off for the Stanley Cup.
The East, with clearly superior talent, rolled to three straight Cups. Beginning with 1970-71 action, the East and West grew to seven teams. Chicago moved to the West and the East added two new teams, Buffalo and Vancouver. The playoffs were now mixed with the #1 and #3 East seed winner facing the West #2 and #4 winner (the West #1 and #3 winner facing East #2 and #4 respectively).
The playoff format was altered after only one year due to speculation of Minnesota throwing games to receive a better seed. The #1 seed teams would face #4 seed and #2 face #3. The NHL grew to eight teams in each division, adding NY Islanders to the East and Atlanta to the West for 1972-73 action. The following year, 1973-74, Philadelphia became the first expansion team to capture the Stanley Cup.
Before the 1974-75 season, the NHL grew to 18 teams. The teams were also realigned geographically to cut travel costs. Two conferences were formed, the Prince of Wales and Clarence Campbell, and two divisions were formed in each. Wales was broken into the Adams and Norris, the Campbell into Patrick and Smythe. Adams had teams in Buffalo, Boston, Toronto and California; Norris with Montreal, Los Angeles, Pittsburgh, Detroit and Washington (new). The Patrick contained Philadelphia, Atlanta, NY Rangers and NY Islanders; while Smythe consisted of Vancouver, St. Louis, Chicago, Minnesota and Kansas City (new). The playoffs were expanded to twelve teams.
Hockey pundits began to claim the NHL grew too fast. With some truth to the pundits, coupled with a late 1970's recession, the NHL did struggle. Kansas City moved to Colorado, California to Cleveland, and Cleveland merged with Minnesota. Much like any other major sport, the NHL had competition from the upstart World Hockey League. As with the (then) recent mergers of the NBA and ABA, and NFL and AFL (basketball and football), the two merged for the 1979-80 season.
Four of the six World Hockey League teams were added to total 21 NHL teams. The four additions were Edmonton, Winnipeg, New England (Hartford), and Quebec. Additional teams meant additional playoffs, the number of teams who saw playoff action increased to 16. A year later Atlanta moved to Calgary. The 1981-82 season saw another geographical realignment and a slowed movement of franchises. For the next ten years, the only movement was Colorado to New Jersey.
From 1991-92 to 1993-94, the NHL added five team (totaling 26), San Jose, Tampa, Ottawa, Florida and Anaheim. The conferences and divisions were renamed to support more geographic terms (Eastern Conference consisted of Atlantic and Northeast division, Western Conference contained Central and Pacific divisions). The 16 team playoff format was altered to the system currently used today. After the latest expansion and promise for future growth, the NHL owners and players went on strike (gasp!).