He was a leading figure in the anti-Vietnam War movement. I consider the success of that movement to be arguably the most important movement in the history of the United States, and possibly more important than either the American Revolution or the Civil War. If there had been no American Revolution, the English colonies would have eventually become independent anyway (like Canada, Australia, New Zealand, India, South Africa, etc.). Most of those places have roughly the same rights that Americans do today, and England itself eventually became a liberal democracy. The primary significance of the Civil War was that it consolidated the US into a northeastern-based capitalist, expansionist empire, and not the abolition of slavery, which would have happened anyway for technological and economic reasons (see Brazil). But the anti-Vietnam War movement was the biggest blow to US imperialism specifically and Western colonialism generally in modern history. It also delegitimized imperialist war in domestic US politics if it requires any sacrifices on the part of Americans (conscription, high casualties, rationing, war taxes, etc.) That’s why all subsequent US imperialist adventures have been paid for with debt and carried out by professional volunteer soldiers and, more often, foreign armies, proxy non-state actors, mercenaries, and technology. Imagine if the George W. Bush regime had been able to field a WW2-level army with tens of millions of people during their “war on terrorism”?
A fearless critic of the American political establishment and a dogged anti-war voice.