Between 1955 and 1975, the United States deployed more than three million military personnel to Vietnam, dropped more bombs on the country than were dropped in all of World War II combined, sprayed twenty million gallons of herbicides over its forests, and lost the war. Roughly 58,000 American soldiers died. Vietnamese deaths — military and civilian, north and south — are estimated at over two million. The war redefined what 'losing' could look like for a global superpower, and what insurgency could achieve against one.
The strategic logic the United States brought to Vietnam was an extension of the containment doctrine: stop communism somewhere, or it would advance everywhere — the so-called domino theory. The Vietnamese Communist leadership, under Ho Chi Minh and his successors, fought a very different war — primarily a war of national independence, second a Marxist revolution. Their tolerance for casualties, their patience for an attritional conflict, and their conviction that they were fighting for their own country against a foreign occupier gave them a mobilization that no amount of American firepower could match. The war's domestic consequences inside the United States were almost as transformative as its foreign ones: the conscription protests, the credibility gap, the Pentagon Papers, the slow erosion of public trust in government, the post-Vietnam reluctance to commit ground troops anywhere — all flowed from this defeat.
Every subsequent American military intervention has been measured against Vietnam: Iraq, Afghanistan, Syria. The lesson the American national security establishment took, eventually, was that air supremacy and superior firepower do not produce political outcomes. Whether the lesson held — or merely got rebranded as 'counterinsurgency' for a generation — is something each ten-year retrospective answers differently.