Complex sentence: In 1877 there was a prevailing feeling in Pittsburgh that the town was suffering at the mercy of unfair pricing from the Pennsylvania Railroad, that had cost the city its preeminence in oil refining, and had privileged Philadelphia at their expense.
Split into simpler sentences: In 1877 there was a prevailing feeling in Pittsburgh that the town was suffering at the mercy of unfair pricing from the Pennsylvania Railroad. The railroad was blamed for costing the city its preeminence in oil refining, and had privileging Philadelphia at their expense.