The National Hockey League added six new franchises for the 1967-68 NHL season, doubling the size of the league. This marked the first change in the composition of the league since 1942, when the Brooklyn Americans folded.
The six teams added were:
For many years after the shakeout caused by the Great Depression and World War II, the NHL owners staunchly resisted applications to expand beyond the so-called "Original Six" clubs: (Boston, Montreal, Toronto, New York, Detroit and Chicago). Groups representing Philadelphia (which had secured rights to the dormant Montreal Maroons franchise), Los Angeles and the AHL Cleveland Barons were each in turn given conflicting requirements that seemed to contemporary observers designed to disqualify the bids, and it was widely understood that the existing NHL owners wanted no encroachments upon their profits. 
The league was an early leader in television broadcasting, both in Canada and the U.S.  However, by 1960, the NHL ended their TV contract, and had none until 1963.  The owners saw that the televising of other sports enhanced those leagues' players image and would provide leverage at salary time. Already players were starting to get lawyers' help in negotiating contracts. The league did not want to change game start times to suit the networks. However, in 1965, the league was told that it would not receive a contract without expansion, and the networks were considering televising games from the Western Hockey League (WHL), an ostensibly minor league that had by that time expanded into several large West Coast markets and accumulated strong rosters by attracting players excluded from the static NHL rosters of that era.
Fears of the WHL becoming a rival major league and the desire for a lucrative TV contract in the US, much like the ones Major League Baseball and the National Football League had secured, wore down the opposition; moreover, as more conservative owners retired, a younger guard more receptive to expansion, such as Stafford Smythe in Toronto, David Molson in Montreal and William Jennings of the Rangers, took power.  All the new franchises, except for the Pennsylvania ones, were outside the northeastern area of the Original Six, and locations were chosen specifically to broaden the appeal of the league. A television agreement reached with CBS specifically called for two of the new teams to be located in California.
Many were upset over the expansion. Canadian fans were irate that no Canadian teams were added, even though Vancouver put forward a bid. Baltimore was also a favorite that did not receive a slot. Politics took a hand in the selections; Vancouver's strong bid reportedly fell to Montreal and Toronto's lack of desire to share CBC TV revenues with another Canadian club, and the powerful Chicago owner's support was reputedly contingent on the creation of a St. Louis team – though no formal bid had actually been received from St. Louis – to purchase the decrepit St. Louis Arena, which the Black Hawks ownership then also owned.
Furthermore, many traditionalists did not like the idea of expansion, claiming it would dilute the talent in the league. Even many of the proponents of expansion were worried at the idea of immediately doubling the NHL's size, instead of easing teams in gradually, as had Major League Baseball. 
Most experts agreed that the new owners paid a heavy price to join the league: the expansion fee was $2 million US, players in the very strict expansion draft were a hefty $50,000, and most teams had no hope of competing successfully with the established teams in the near future. One advantage of the expansion, however, was that the new teams were all placed in the newly-formed West Division, and as the final round of the playoffs, an expansion team was guaranteed a slot in the Stanley Cup finals.
The new teams offered a big change to the league. After seeing virtually the same red/blue/black uniforms for over twenty years, purple, green, sky blue, and orange were introduced.  In fact, the California Seals even wore white skates during the time in which they were owned by Charles Finley. By the mid-1970s, five of the six teams would find success, with the Philadelphia Flyers winning the Stanley Cup in 1974 and 1975. The California Seals franchise, uncompetitive both on the ice and at the box office, was moved to Cleveland and became the Barons in 1976, and then merged with the Minnesota North Stars (now the Dallas Stars) in 1978.
The expansion was the end of the Original Six era, and the beginning of the modern era of the NHL. There would be further expansions in 1970, 1972 and 1974. The expansion, Bobby Orr's record contract, and the World Hockey Association forever changed the landscape of the North American professional game.