The Big East launched its inaugural season in 1979-1980 with Syracuse, Georgetown, St. John's, Connecticut, Providence, Seton Hall, St. John's and Boston College on board. Villanova would join a year later, and Pitt a few years later in 1982.
It may be hard to believe now, but the Orangemen did not have rivalries with all those teams prior to the Big East. A few, including Georgetown, they had barely played. I discussed that in detail in an article back in 2018.
The Orangemen did have some common opponents prior to the Big East. Penn State was the most common opponent over the previous 11 seasons (1968-69 to 1978-79), with 23 games.