Writers have praised President Lyndon B. Johnson's ‘Great Society’ anti-poverty measures and his civil rights legislation, but there has been much less enthusiasm for his handling of foreign affairs. This reticence is largely due to the Vietnam War. Johnson sent American combat troops to support South Vietnam in 1965, but despite the presence of over half a million US soldiers by 1968 no victory was in sight. By the time the last American soldiers were withdrawn in 1973, some 58,000 American lives, plus countless times more Vietnamese ones, had been lost. South Vietnam collapsed in 1975. The military intervention generated powerful anti-war and countercultural movements, brought about the vilification of the political institutions and gave rise to an anti-interventionist ‘syndrome’ in US foreign policy. Philip Geyelin wrote in 1966 that Johnson was ‘a swashbuckling master of the political midstream, but only in the crowded, well-traveled familiar inland waterways of domestic politics. He had no taste or preparation for the deep waters of foreign policy.’ Johnson was ‘king of the river and a stranger to the open sea’. According to Robert Dallek, the expansion of the commitment in Vietnam rested on ‘a combination of noble and ignoble motives that little serve’ Johnson's ‘historical reputation’ and led to ‘the worst foreign policy disaster’ in American history.

Thomas Alan Schwartz has noted that the debacle in Southeast Asia has led many historians to depict Johnson as the ‘ugly American’ – crude, provincial and lacking in subtlety in the conduct of foreign policy.