After nearly two months of trench warfare and artillery bombardment across the mountains of northwestern Vietnam, General Vo Nguyen Giap's Viet Minh forces overwhelmed the last French positions at Dien Bien Phu. Some 11,000 French and colonial troops surrendered. The defeat shattered French confidence in the war and led directly to the Geneva Accords partitioning Vietnam, setting the stage for later American involvement.
The French had chosen Dien Bien Phu, a remote valley near the Laotian border, believing its airstrip and superior firepower would let them lure the Viet Minh into a conventional battle they could win. They badly misjudged Giap's logistics: Vietnamese laborers and bicycle porters hauled artillery pieces piece by piece up jungle mountainsides and dug them into camouflaged positions overlooking the French garrison, a feat French intelligence thought impossible.
The siege began in March 1954. French artillery officer Colonel Charles Piroth, who had promised the enemy guns would never fire more than a few rounds before being silenced, killed himself with a grenade days into the bombardment once he realized how badly he'd miscalculated. Monsoon rains flooded the trenches; wounded men drowned in mud.
When the final Viet Minh assault broke through on May 7, the white flag went up over the French command bunker. The defeat, coming just as the Geneva Conference on Indochina opened, forced France to abandon its colonial war. Vietnam was split at the 17th parallel — a division intended to be temporary that instead hardened into the fault line of the next two decades of war.