It is difficult to assess which side had the better of this debate during the Vietnam War. The decision to send combat forces to Vietnam initially appeared to enjoy high levels of public support, and the National Party did not suffer unduly adverse electoral consequences, being returned to office twice - in 1966 and 1969 - during the Vietnam period. Nor was the government ever sufficiently concerned by domestic criticism to change a policy it had adopted largely for alliance reasons.
On the other hand, despite having no decisive impact on official policy-making and arousing hostility from some New Zealanders, the anti-war movement drew growing support, especially during the closing stages of the Vietnam War. This support was illustrated most visibly during the 'mobilisations' of the early 1970s, when thousands marched in protest against the war in all the country's major centres. The Vietnam conflict thus brought with it a polarisation of opinion and a questioning by many New Zealanders of the government's alliance policies, especially among younger people in higher education during these years - the so-called Vietnam Generation.
Another significant domestic impact of the critique championed by the anti-war movement was that one of the two major political parties came to embrace many of its premises. The Labour party was initially more cautious in opposing official policy on the Vietnam conflict. The party had stressed humanitarian and economic aid as more important than military action in helping to resolve Vietnam's problems from the early 1960s. Yet once New Zealand combat forces were sent, party leaders were reluctant to advocate immediate withdrawal, perhaps because of concerns about likely electoral consequences.
Labour's policy on Vietnam firmed considerably after 1966. By 1969, its leader, Norman Kirk, had made an unequivocal commitment to withdraw if victorious in that year's election, but National was re-elected. Thereafter, Labour asserted its opposition more confidently, sensing it was now on the more popular side of the issue and seizing on the Americans' own progressive disengagement from Vietnam as vindication of its policy. Since almost all New Zealand troops had left Vietnam before the November 1972 election, the new Labour government's prompt withdrawal of the remaining training teams caused little controversy.
If of limited practical significance after 1973, Labour's and National's divergent policies on Vietnam symbolised wider differences about national security. National continued to accept the orthodoxies of alliance reasoning on which its Vietnam policy was based. In contrast, Labour leaders called for 'new thinking' in foreign policy that would allow New Zealand to pursue a more independent course in world affairs, that would incorporate a 'moral' dimension, and that would better reflect the country's character as a small multiracial nation in the South Pacific. Having rejected the Vietnam policy of New Zealand's major alliance partner, Labour's leaders did not repudiate ANZUS - as many anti-war activists and party members urged. Instead, they sought to sanction a position of dissent within the alliance framework, analogous to the line of argument which would later be used to justify the fourth Labour government's policy of opposing nuclear ship visits. Such qualifications notwithstanding, Labour's stance on the Vietnam War broke the previous bipartisan, Cold War consensus on foreign policy.
The Vietnam War thus marked a turning point in the evolution of New Zealand's post-war foreign and security policies. In terms of national security doctrine, combat involvement in Vietnam represented the culmination of a line of official thinking based on the primacy of the ANZUS alliance, the acceptance of stark assumptions about the menace of Asian communism, and the cogency of forward defence in South-east Asia.
While privately dubious about the wisdom of a massive military effort in Vietnam, the Holyoake government showed that it was committed to the shared alliance strategy of containing communism in South-east Asia. It offered public support for American policy and contributed token combat forces in Vietnam as the price of continued participation in that strategy. The outcome of the Vietnam War, however, created a crisis for the alliance policy and several of its elements - most notably a strong forward defence posture in South-east Asia - were adjusted in the aftermath of that conflict. In large part, that readjustment was due to the re-evaluation of American regional strategy in the form of the Nixon Doctrine.
The Vietnam experience was thus also important as a test of the country's interaction with its major post-war ally. On the one hand, the National government's policy staved off any confrontation with Washington of the sort which would cause the suspension of the American security guarantee to New Zealand in the 1980s. To that extent, the Holyoake government attained the central objective of its Vietnam policy and the alliance with the United States remained intact at the end of the war. On the other hand, the alliance relationship was less firmly rooted on a popular level, with significant numbers of New Zealanders coming to oppose perceived subservience to the United States in security matters.