When Saad Hariri resigned his post as prime minister of Lebanon last week, the move surprised even his closest associates. The normally soft-spoken premier lashed out at Iran and Hezbollah, accusing them of plotting his assassination, and vowing that the region’s reawakened Arabs would “cut off” Tehran’s arms. The unusual resignation came amid internal upheavals within Saudi Arabia and escalating Saudi-Iranian tensions over Lebanon and Yemen, fueling speculation that all were somehow related.

On the morning of October 23, 1983, Imad Mughniyeh and Mustafa Badreddine perched atop a building in south Beirut, binoculars fixated on the four-story U.S. Marine barracks attached to the International Airport.