The United States needed allies in the Vietnam War. In May 1964, it launched the ‘more flags’ campaign to persuade other countries to join the conflict, hoping that its initiative would help define the contest as a Cold War crucible, deflect charges of US colonialism in the region, and justify mounting sacrifices at home. While ‘more flags’ could help with results on the battlefield, Washington viewed it more symbolically. As President Lyndon Johnson purportedly told British Prime Minister Harold Wilson in asking for London’s participation: ‘a platoon of bagpipers would be sufficient, it was the British flag that was needed.’

Initially, the United States viewed ‘more flags’ primarily as a way to secure economic assistance, military advisors, and humanitarian aid from countries of the so-called free world. But, after the United States committed its first combat troops in March 1965, Washington wanted allied contributions to mirror its own. That meant boots on the ground. The United States went on to find success in the Asia-Pacific region. Over the course of the war, the United States secured hundreds of thousands of soldiers from Australia, New Zealand, South Korea, Thailand, and the Philippines.

If 20th-century history served as any precedent, the United States should have found success in Latin America, too. During the First World War, Brazil’s navy entered the war on the Allied side, patrolling the South Atlantic for German U-boats. During the Second World War, Brazil sent its army, navy, and air force to fight on the Allied side in Italy and the Battle of the Atlantic, suffering over a thousand casualties. Mexico also joined, sending an air squadron known as the Aztec Eagles to fight Japan in the Philippines. During the Korean War, Colombia contributed troops to the US-led United Nations coalition.

As the United States cast its gaze around the region to find a fighting force for Vietnam, prospects looked bleak. Reports from Argentina and Venezuela, for example, indicated that leaders would be unwilling to take the domestic political risk. US ambassadors warned against even raising the issue. Increasingly, only one state appeared worth pursuing: Brazil.

By early 1965, US-Brazil relations were on the upswing. The installation of the US-backed military dictator Humberto Castelo Branco in a coup the previous year moved Brazil away from a more independent foreign policy towards greater alignment with the United States. ‘What is good for the United States is good for Brazil’, asserted the country’s Ambassador to Washington, an exaggeration that captured the zeitgeist. Tangible military results ensued. That spring, Brazil deployed over 1,300 troops in support of a US-led anti-communist intervention in the Dominican Republic. The United States wanted a similar commitment for Vietnam.

In December 1965, top US officials considered linking an annual $150 million economic loan to Brazil with a request for soldiers. When officials split over the idea, National Security Advisor McGeorge Bundy, an instigator of the scheme, took it to Johnson for a final decision. In a meeting in the Oval Office, Bundy made clear to Johnson that the United States was ‘not trying to blackmail Castelo Branco’ with the loan, but he wanted to go to Brazil’s leader with it and make clear the US need for a Brazilian military commitment in Vietnam. In Bundy’s mind, Castelo Branco was the ‘kind of fella’ to appreciate the implicit trade-off. Johnson agreed with the tactic. He rejected any strict quid pro quo that might force Castelo Branco to refuse economic assistance, but he wanted to go ‘to the bottom of the barrel’ and ‘use everything’ to convince Brazil to supply forces. Washington sought roughly a thousand soldiers from Brazil, and cabled US Ambassador Lincoln Gordon to make it happen.

In a meeting with Castelo Branco a week later, Gordon asked what it would take to get Brazil to deploy a battalion for the war. Castelo Branco demurred. Brazil’s Congress would have to approve any force contributions, he explained, but had recessed for months. Surely the United States did not want him to do something unconstitutional.

Castelo Branco believed that Brazil’s soldiers in the Dominican Republic already constituted a sacrifice for the war effort, as it could help free up US forces to fight in Southeast Asia. Nevertheless, he promised to further reflect on the domestic and international dynamics of Gordon’s request. Nothing immediate came of it, and the loan went through without an answer.

Over the following year, momentum built in Brazilian ruling circles for a military contribution. Some officials liked the potential to glean insights in counter-revolutionary warfare against communist insurgents. The lessons drawn from fighting in a tropical theatre similar to Brazil had the potential to be applied at home. With that in mind, Brazil’s minister of war requested that military attachés from the three branches of the armed forces be posted to Vietnam.

The greatest Brazilian initiative, though, came from Manoel Pio Corrêa, the influential Secretary General of Brazil’s Foreign Ministry. On 30 December 1966, Pio Corrêa lunched at Brazil’s foreign ministry with John Tuthill, Gordon’s replacement as US Ambassador, and a top naval officer from each side. During the meal, Pio Corrêa complained about the state of Brazil’s navy. He thought its deteriorating hardware hurt morale and that a decline in its stature, being a foundational conservative institution, could upset the country’s internal stability.

The Brazilian then pushed a request he had toyed with for some time: two modern destroyers under a lend-lease program. In exchange, he shared, Brazil would stumble into the Vietnam War.

Pio Corrêa explained that Brazil could acquire the destroyers in Honolulu and take them on a ‘shakedown cruise’ alongside US naval forces to Vietnamese waters. The destroyers would then arrange to be fired upon by North Vietnam so that Brazil could enter the conflict. Pio Corrêa seemingly had the approval of Brazil’s navy and Castelo Branco. It left Tuthill with the impression that the United States had ‘a fair chance’ of obtaining a Brazilian naval contribution for the war effort.

But Latin American boots stayed back for the duration of the conflict. In Brazil, public opinion drove the decision. Anti-war protests sprang up across the country, but the threat of public opinion loomed larger. Brazil’s leaders feared a ‘public explosion’ if it committed to fight in Vietnam.

Brazilian nationalism mattered, too. Brazil’s leaders disliked that Brazilian forces in Vietnam might be denigrated as US mercenaries and at times used abstention for domestic political gains. Such factors particularly mattered for General Artur da Costa e Silva, who succeeded Castelo Branco as Brazil’s leader in early 1967.

Limits existed for the United States, too. The State Department disliked the imprecision of Pio Corrêa’s proposal and sought to attach strings, namely, an up-front commitment of at least a year of patrols and $10 million in retrofits for the destroyers. More broadly, it became apparent that the United States would need to rewrite its relationship with Brazil to prioritise it in hemispheric relations. That promise remained unfulfilled from earlier joint interventions and needed resolution, local officials reminded Tuthill, but the Johnson administration stayed noncommittal.

Conversely, some US officials thought Brazilian – or any Latin American – troops in Vietnam would wreak havoc on inter-American relations.

This spring marked the 50th anniversary of the fall of Saigon and the ultimate demise of the US war effort in Vietnam. Would Latin American soldiers have made a difference in the outcome? Almost certainly not. But the quest to get Latin America to fight in Vietnam illustrates important power dynamics. It raises questions about what it takes to get an ally to fight overseas and suggests a need to fulfil both short-term tactical demands and longer-term strategic priorities. It also underscores the threat domestic public opinion can pose to dictatorships, even those that remain in power for decades.

Finally, this episode is a reminder of the limits that can exist in US-Latin American relations. Amid asymmetries of power, neither the United States nor Latin America could find the right formula for action.

In the end, Latin American leaders’ refusals to join the United States was the best possible outcome. As Gordon later reflected on the push to get Latin American nations to fight in Vietnam: ‘It would have been a disaster.’