Opposition to United States involvement in the Vietnam War An infamous photo of General Nguyễn Ngọc Loan shooting an alleged terrorist in handcuffs during the Tet Offensive also provoked public outcry. Another element of the American opposition to the war was the perception that U.S. intervention in Vietnam, which had been argued as acceptable because of the domino theory and the threat of communism, was not legally justifiable. Some Americans believed that the communist threat was used as a scapegoat to hide imperialistic intentions, and others argued that the American intervention in South Vietnam interfered with the self-determination of the country and felt that the war in Vietnam was
Non-intervention in the Spanish Civil War follow a policy of non-intervention, but did not announce it officially. This isolationism on the Spanish war would later be identified as disastrous by Under-Secretary of State Sumner Welles. Five days later, the Glenn L. Martin Company enquired whether the government would allow the sale of eight bombers to the Spanish Republican Air Force; the response was negative. It also confirmed it would not take part in several mediation attempts, including one by the Organization of American States. Mexico soon became the first nation to openly support the Republicans. On 15 August, the United Kingdom banned exports of war material