How did North Vietnam defeat South Vietnam in 1975?

North Vietnam’s victory in 1975 was the culmination of a rapid military collapse of the South Vietnamese government and army, driven by internal instability and the withdrawal of U.S. support.12

Following the 1973 Paris Peace Accords, the South Vietnamese government faced severe economic crises, rampant inflation, and widespread corruption. These issues, combined with the loss of U.S. military and economic aid, led to plummeting morale and high desertion rates within the Army of the Republic of Vietnam (ARVN).12

In early 1975, North Vietnam launched a major offensive. After a successful test of South Vietnam's defenses at Phuoc Long, the North Vietnamese army advanced into the Central Highlands. A poorly executed retreat ordered by President Nguyen Van Thieu turned into a rout, causing panic and further disintegration of the South's military.12

By April, North Vietnamese forces encircled Saigon. Following Thieu’s resignation, the South Vietnamese government surrendered unconditionally on April 30, 1975, as North Vietnamese tanks entered the capital. This victory effectively ended the 30-year struggle for control over Vietnam.12