BAGGAO, Philippines—Black Hawk and ATAK helicopters swooped overhead and began firing into the mountains on an early February afternoon. Farmers tilling crops and tending their water buffalo ran for cover, taking shelter as the helicopters strafed the area. In a nearby town square, onlookers recorded with their phones, gasping as explosions ripped across the horizon. A Bell AH-1 Cobra attack helicopter later made rounds in the area, witnesses said, as soldiers sequestered farmers in shelters. They were kept from their farms for weeks as their harvest wilted and died.