Complex sentence: During the 1960s, the WHL moved into large west coast markets like Los Angeles and San Francisco, and it was fears that the WHL would become a rival major league that finally convinced the National Hockey League to expand for the 1967-68 season.
Split into simpler sentences: During the 1960s, the WHL moved into a number of large west coast markets including Los Angeles and San Francisco. It was fears that the WHL would become a rival major league that finally convinced the National Hockey League to expand for the 1967-68 season.