In 1972, the Pittsburgh Steelers were a franchise that had never been relevant. The next eight seasons changed all that. With one of the great defenses of all time, the Steelers ripped off a run of eight playoff berths, six AFC Championship Game trips and four Super Bowl trophies. They were not only dominant, but they changed the complete arc of their franchise history. Read all about eight seasons, including the development of Terry Bradshaw, the rise of Franco Harris and…