The modern Saudi–Iranian rivalry cannot be understood through the narrow lens of the 1979 Revolution alone. Its foundations were laid decades earlier, during the formative periods when both states emerged as centralized monarchies controlling vast oil wealth and claiming leadership over competing visions of Islamic legitimacy. While their parallel trajectories toward petro-state power created structural similarities, the paths they followed also planted the seeds of future confrontation. Understanding how Saudi Arabia and Iran became regional powers reveals why their rivalry proved so persistent and why it resisted resolution for over four decades.