When the final phase of peace negotiations in Paris broke down, President Nixon ordered the start of Operation Linebacker II, the maximum force bombing of Hanoi and Haiphong, the two major North Vietnamese population centers.

After 11 days, during which 100,000 bombs were dropped, five American bombers were brought down by surface-to-air (SAM) missiles and an estimated 1,320 civilians died, both sides agreed to a cease-fire.  All American prisoners of war were to be released within two months, and some 150,000 North Vietnamese troops remaining in the South were allowed to stay.