In the 1940s and early 1950s, the Cold War convention of containment, which undergirded American involvement in Vietnam, was broadly shared, internalized, at times even fostered, by the United States European allies. This consensus broke down by the 1960s, as successive US administrations saw themselves locked ever more rigidly into Cold War logic which seemed to require going to war to preserve a noncommunist South Vietnam. By contrast, the United States transatlantic allies and partners increasingly came to question the very rationale of US intervention. By the mid-1960s there was a remarkable consensus among government officials across Western Europe on the futility of the central objective of the American intervention in Vietnam of defending and stabilizing a noncommunist (South) Vietnam. European governments refused to send troops to Vietnam. However, West European governments differed considerably in the public attitude they displayed toward US involvement in Vietnam, ranging from France’s vocal opposition to strong if not limitless public support by the British and West German governments. Across Western Europe, the Vietnam War cut deeply into West European domestic politics, aggravated political and societal tensions and diminished the righteousness of the American cause.

In their opposition to American imperialism, radicals pursued many actions. They synchronized protests, helped deserting GIs find safety, strengthened ties with Vietnamese revolutionaries, put the United States on trial for genocide, and even organized international brigades to fight in Vietnam. But at this stage, they prioritized the ideological struggle, which was precisely what Vietnamese officials themselves sought most from their comrades in this part of the world. Indeed, Vietnamese revolutionaries believed that the war would be fought not only in the jungles of Vietnam but on the terrain of ideas. Collaborating closely with Vietnamese communists, radicals in the North Atlantic radicalized the discourse around the war. In fact, by the end of 1967, the general antiwar struggle grew far more radical. Radicals defined the enemy as imperialism, coded their internationalism as anti-imperialism, and revived the Leninist problematic of self-determination. This approach to internationalism became so popular that even those who did not consider themselves radicals adopted some of its core elements. By the late 1960s, anti-imperialism was beating out its many internationalist rivals – such as individualist human rights – to become the dominant way in which activists in the North Atlantic imagined international change.