50 years on, lessons from Vietnam's Tet Offensive have been forgotten
1968 Tet Offensive holds lessons for US wars in Afghanistan and Iraq
In January 1968, Vietnamese revolutionaries launched a series of military attacks known as the Tet Offensive.
It was a strategic masterstroke that shattered the myth that the US could win the war.
Its aftermath effectively toppled an American president, and forced a new president to seek withdrawal of US forces, allowing the North Vietnamese to seize victory in 1975.
The lessons of the attacks during the Tet Lunar New Year festival are just as relevant today for both the US and its enemies in the Middle East.
The war in Afghanistan has entered its 17th year, with defeat staring the US in the face as it has proved unable to fight a guerrilla war.
Besides, Afghanistan presents its own lessons, having defeated several imperial powers in the past.
During Tet, the combined forces of the North Vietnamese army and the National Liberation Front of South Vietnam (NLF) attacked more than 100 cities and towns in the south, as well as the US embassy in Saigon and the imperial city of Hue.
A triumphant North Vietnamese General Tran Van Tra declared that the Tet Offensive was a definitive turning point in the war.
After Tet, the US gave up on winning the war and sought an exit through peace talks at which Hanoi held the trump card. Under the peace agreement with the US in 1973, North Vietnam retained its troops in the south while requiring the US to withdraw theirs.
Tet exposed the false claims of President Lyndon B Johnson and US General William Westmoreland, who had been telling the American people that there "was light at the end of the tunnel" and that the US strategy of attrition was working.
Anti-war protests escalated after Tet, and as his policy lay in tatters, President Johnson made a stunning announcement on March 31, 1968, that he would not run for a second term.
Historian David Elliott believes there were "two great lessons of Vietnam" that the Trump administration should remember.
The first was formulated by McGeorge Bundy, President Johnson's national security adviser, after the end of the Vietnam War: "We ought not to ever be in a position where we are deciding, or undertaking to decide, or even trying to influence the internal power structure" of another country.
The second lesson of Vietnam was articulated by Henry Kissinger, then an adviser to Mr Johnson, in an essay in Foreign Affairs at the end of 1968: That it is difficult for a superpower to combat a guerrilla force.
"We fought a military war; our opponents fought a political one," Dr Kissinger wrote.
"We sought physical attrition; our opponents aimed for our psychological exhaustion. In the process we lost sight of one of the cardinal maxims of guerrilla war: The guerrilla wins if he does not lose. The conventional army loses if it does not win."
Even 50 years later, the lessons of the Tet Offensive are still relevant in Afghanistan, Iraq and the wider region, where small, guerrilla-style armies are waging war.
The writer is a former BT Senior Indochina Correspondent who has written extensively on the Vietnam War.