The Tet Offensives of 1968 and 1969 destroyed the Viet Cong as a viable military entity, and forced Gen. Vo Nguyan Giap to move PAVN regular units into South Vietnam to take their place. 1969 was an unsuccessful rebuilding year for the Communists in South Vietnam, and they couldn’t prevent the US and South Vietnamese invasions of Laos and Cambodia in 1970 which caused serious damage to hitherto untouchable PAVN base camps in those countries. PAVN’s weakness and the disruption of the Ho Chi Minh Trail gave Gen Creighton Abrams, the new commander of the Military Assistance Command – Vietnam, the opportunity to implement new tactics in Vietnam dubbed the “Inkblot Strategy”. American and ARVN troops secured the cities, town, hamlets, and then the countryside of S. Vietnam through counterinsurgency tactics the way ink blots spread on a piece of paper. (Combined with targeted strikes on high value targets and training of South Vietnamese troops and militias). From 1969 through 1972, the strategy was successful, and with President Richard Nixon’s policy of Vietnamization, the ARVN took over security of the country. Almost all American combat troops left Vietnam by the autumn of 1972.
Though Abrams’ strategy was successful, the South Vietnamese still needed American advisers, air support, supplies, and financial assistance to deal with the conventional PAVN attacks. The war in the south was being waged almost exclusively by North Vietnamese regular troops, not the indigenous Viet Cong. Contrary to what you learned in university, the PAVN were almost as alien to the South Vietnamese as the Americans. Giap decided to gamble on a conventional assault similar to the one that almost overran the south in 1964. However, Giap underestimated the destructiveness of the remaining American firepower, and the professionalism of ARVN, which by 1972 was relatively well trained and equipped. With American assistance, South Vietnam repelled North Vietnam’s spring offensive in 1972, the Easter Offensive, and inflicted debilitating casualties on forces that Giap had painstakingly concentrated throughout 1971.
With the North Vietnamese defeat during the Easter Offensive, the Paris Peace Talks took on a new fervor. By October, the US and North Vietnam had reached an agreement, but South Vietnam’s President Theiu would not sign, because he felt the US would abandon South Vietnam after the cease fire so he wanted better terms in case South Vietnam had to fight on itself. Theiu proposed many changes to the cease fire document, which convinced the North to renegotiate all the points in full to get their own better terms. Both sides infuriated Nixon. On 14 December 1972, the talks ceased completely when the North Vietnamese walked out and would not commit to a resumption of negotiations. Nixon sent North Vietnam an ultimatum to resume talks within 72 hours. Nixon needed a cease fire because the newly elected Democratic majority in the 93rd Congress would begin sessions just after New Year’s. They threatened to end all support to South Vietnam if there was no cease fire.
After the ultimatum deadline passed on 17 December, Nixon ordered Operation Linebacker II to bring the North back to the bargaining table and more importantly convince Theiu that America wouldn’t abandon his country after the cease fire. Unlike previous bombing campaigns, Linebacker II was a “maximum effort” and no targets not covered in Law of Land Warfare were off limits. Linebacker II would not consist of strictly tactical air support, but would unleash B-52’s over Hanoi and Haiphong. Furthermore, Nixon authorized the mining of Haiphong harbor which was the primary entrance point for support by North Vietnam’s primary sponsor, the Soviet Union. By 1972, the “Chinese” faction inside the North Vietnamese Communist Party had been thoroughly discredited by the defeats in 1968 and 1969. And the Sino-Soviet Split was permanent after Nixon’s policy of rapprochement culminating with his visit to China in February 1972. (China and Vietnam would eventually go to war in 1979.)
Starting the morning of 18 December, Operation Linebacker II pounded targets in North Vietnam. North Vietnamese infrastructure was smashed. But the repetitive and unimaginative nature of the strikes allowed the North Vietnamese to anticipate the third day’s strike and its Soviet-manned air defenses shot down several B-52s and other aircraft. Even worse a poorly placed B-52 strike destroyed a hospital outside Hanoi which galvanized the peace movement in America. Nevertheless, Nixon wasn’t backing down and ordered the US Air Force and Navy to continue strikes across North Vietnam. A-7 Corsair IIs from carriers in Gulf of Tonkin, F-4’s from bases in Thailand, and B-52s from Guam and the Philippines struck airfields, bridges, power plants, air defenses, storage areas, and military bases across the country. The operation was only supposed to last three days, but continued until 30 December. On 29 December, Hanoi asked to resume talks on the 2nd of January. That evening, Nixon ordered air operations against North Vietnam to cease the next day.
The next day, on New Year’s Eve 1972, Gen Giap wrote in his diary, “We have lost the war”.
On 27 January 1973, both North and South Vietnam accepted the original October 1972 draft of the Paris Peace Accords cease fire documents.
It didn’t matter. Though US ground troops were effectively out of the war, both Vietnam governments broke the accords almost immediately and both the US and the Soviet Union continue to supply their respective partners. Despite South Vietnam defeating Communist offensives in 1973 and 1974, the US Congress ceased all aid in 1975, and the well supplied PAVN forces overran the country that spring. Saigon fell on 29 April 1975.