What does it mean to stand in solidarity with a place you've never been? The Vietnam idea explores how, during and after the American War in Vietnam, artists, activists, and movements around the world reimagined Vietnam as a symbol of global and local resistance - transforming it into an idea more than a place. From posters and protest actions to conceptual art and underground film, this interdisciplinary study shows how Vietnam became a proxy through which global leftist struggles against colonialism, racism, and imperialism were visualised and made politically legible. Traversing archives in Vietnam, Jordan, Australia, and beyond, Brynn Hatton uncovers how the image of Vietnam circulated in radical aesthetic projects, often generating powerful affective solidarities across geographic and political borders. It also produced unintended effects, as protest art often mirrored the very visual logics of empire it sought to dismantle. The Vietnam idea asks urgent questions about the politics of analogy, the limits of globalism, and the afterlives of revolutionary art.