The Nixon administration's strategy for ending the American military commitment in Vietnam — known in the strategy's public form as Vietnamisation, and in its private form as the simultaneous pursuit of a negotiated settlement with North Vietnam, the gradual transfer of combat responsibility to ARVN, the secret expansion of the war into Cambodia and Laos, and the maintenance of substantial American air power as a continuing coercive instrument — produced, across four years, the substantive American military withdrawal and the negotiating framework that would, in January 1973, formally end the American combat commitment. It also produced, as a substantive matter, the conditions under which the South Vietnamese government would face the 1975 PAVN final offensive without sufficient American material or political support to survive it. The four-year Nixon period was the substantive deathbed of the South Vietnamese state — although the patient continued, with progressively reduced vitality, to function until April 1975.
The Nixon doctrine
The Nixon doctrine, articulated by the new president at Guam on the 25th of July 1969, was the foundation of the broader strategic-political reorientation. The substance: the United States would honour its existing treaty commitments, would provide a nuclear umbrella, and would provide military and economic assistance to allies threatened by aggression — but it would not assume primary responsibility for the defence of allied states. The application to Vietnam was that ARVN would, across the next several years, assume primary combat responsibility, with American forces progressively withdrawn. The first American troop reductions began in July 1969 with the withdrawal of 25,000 troops; further reductions of 60,000 in 1970, 150,000 in 1971, and substantially all remaining combat units in 1972 produced a total reduction from the 540,000 peak of 1968 to approximately 25,000 by January 1973.
The simultaneous Vietnamisation programme attempted to compensate for the American withdrawals by substantial increases in ARVN equipment, training and organisational capacity. ARVN's order of battle was expanded; new equipment (M48 tanks, F-5 aircraft, modern artillery) was transferred; American advisory presence was reorganised to focus on capability development. The substantive results were mixed. ARVN's tactical capabilities improved measurably across 1969-71; its strategic-operational capabilities, its officer corps quality, its supply discipline, and its political-administrative integrity remained substantially limited. The fundamental problem was that the South Vietnamese state's military performance was constrained by the underlying political weakness of the Thieu regime — which Vietnamisation could not address.
Cambodia
The Cambodian incursion of April-July 1970 — Nixon's most controversial decision of the period — was the substantive expansion of the war into the previously formally neutral Cambodian state. The military objective was to destroy the PAVN sanctuaries in the Cambodian border regions that had served, since the early 1960s, as the principal cross-border bases for operations into the southern South Vietnamese provinces. The political-diplomatic prelude was the Cambodian coup of the 18th of March 1970, in which the right-wing General Lon Nol overthrew the neutralist Prince Norodom Sihanouk; the Lon Nol government tacitly authorised American and ARVN incursions into Cambodian territory.
The operations of April-July 1970 involved approximately 50,000 American and ARVN troops crossing into the Fishhook and Parrot's Beak regions of eastern Cambodia. The substantive military results were modest: substantial quantities of PAVN supplies and equipment captured, several PAVN command facilities overrun, but the principal PAVN forces had withdrawn deeper into Cambodia in anticipation of the incursion and the strategic damage to PAVN operational capacity was limited. The political costs in the United States were substantial: the American student protests against the incursion produced the National Guard shootings at Kent State University in Ohio on the 4th of May 1970 (four students killed) and at Jackson State College in Mississippi on the 14th-15th of May (two students killed); the Senate revoked the Gulf of Tonkin Resolution in June 1970 (though the revocation did not affect the Nixon administration's constitutional position on the war's continuation); the substantial American public consensus against further escalation hardened.
The longer-term consequence of the Cambodian operations was the substantial Khmer Rouge expansion across the Cambodian countryside under the chaos produced by the war's extension into Cambodia, the destabilisation of the Sihanouk-era political settlement, and the eventual Khmer Rouge takeover in April 1975. The Cambodian secondary war — including the substantial American B-52 bombing of Cambodian territory across 1969-1973, and the eventual Khmer Rouge revolutionary terror of 1975-1979 in which approximately 1.7 million Cambodians died — is a long subject not within this volume's scope. The point for South Vietnamese history is that the Cambodian theatre's instability further complicated the strategic-operational picture across 1970-73 without producing the decisive military advantage that the 1970 incursion's planners had hoped for.
Laos
The complementary Laotian campaign — the ARVN incursion into Laos of February-March 1971, designed to interdict the Ho Chi Minh Trail in the panhandle of Laos — was a substantial ARVN operational failure. The operation, Lam Son 719, deployed approximately 17,000 ARVN troops across the Laotian border without American ground-force support (American forces being prohibited by the Cooper-Church Amendment of December 1970 from operating in Laos). The PAVN defensive response, prepared in advance by extensive intelligence on the operation, produced an ARVN tactical reverse: substantial ARVN casualties (approximately 8,000 in six weeks), loss of substantial American-supplied equipment, and substantial damage to ARVN morale and reputation. The operation was the principal field test of Vietnamisation in 1971 and produced a substantially less reassuring result than its planners had hoped.
The 1972 Easter offensive
The PAVN 1972 Easter offensive — the conventional-armoured invasion of the south that opened on the 30th of March 1972 — was the most substantial military test of the Vietnamisation programme. PAVN forces, equipped with substantial Soviet armoured and artillery materiel, crossed the demilitarised zone in three principal axes: across the seventeenth parallel into Quang Tri province in I Corps; across the Cambodian border into Binh Long province in III Corps north of Saigon; and across the central highlands into Kontum and Binh Dinh. The offensive overran Quang Tri city by the 1st of May, besieged An Loc and Kontum from mid-April, and produced the most substantial military crisis of the post-1968 period. The American response was the substantial application of air power: B-52 strikes against PAVN concentrations, the renewed bombing of North Vietnam (Operation Linebacker I, May-October 1972), and the naval mining of Haiphong harbour and other North Vietnamese ports. The combined air and naval pressure substantially attrited the PAVN offensive across May-September 1972; ARVN counter-offensives recovered Quang Tri city by September; An Loc and Kontum held.
The 1972 Easter offensive demonstrated that ARVN, with sufficient American air support, could defeat a conventional PAVN offensive — but that without American air support, the ARVN performance would have been substantially worse. The substantive lesson for North Vietnamese planners was that the elimination of American combat air power would be a prerequisite for any future final offensive; the substantive lesson for American planners was that air power could substitute for ground troops in the short term but could not, indefinitely, compensate for the political weakness of the South Vietnamese state. The Paris negotiations that produced the January 1973 settlement are the next chapter.
End of Chapter VI