By Matthew Davis
BBC News website
US President George W Bush has invoked the "tragedy of Vietnam" to warn of the consequences of a hasty pull-out from Iraq.
Mr Bush is invoking the past to warn of the dangers of a hasty retreat
His comments will generate much debate as to how alike the conflicts really are, but it is clear their differences are many.
More than half a million US troops were on the ground in Vietnam, fighting the communist North, at the peak of the eight-year US military involvement.
By the time the last US soldier left in 1973, the conflict had cost the US more than 58,000 lives. About four million Vietnamese civilians were killed.
The conflict had become very divisive at home. It remains a complex and painful subject for millions of Americans.
Today in Iraq the US's commitment is much smaller (about 160,000 troops) and casualties have been fewer (about 3,700 US dead).
The aim is to leave with heads held high much sooner.
But while the scale of Vietnam may dwarf Iraq, President Bush says there is a similarity with "particular significance", as US leaders again face increasing pressure for a quick pull-out from a very unpopular war.
He says the "unmistakable legacy of Vietnam is that the price of America's withdrawal was paid by millions of innocent citizens whose agonies would add to our vocabulary new terms like 'boat people', 're-education camps' and 'killing fields'".
The president is invoking some dark pages from the history books to warn of the consequences of leaving Iraq too soon.
Iraq is a country divided, but in a different way to Vietnam
Two years after the US withdrawal, the North Vietnamese launched a full-scale invasion of the South, which had been supported by US forces and air power. The South soon surrendered.
In the aftermath, many thousands of South Vietnamese were imprisoned in "re-education camps". Tens of thousands died. More than two million people fled Vietnam. The plight of these "boat people" became an international humanitarian crisis.
Neighbouring Cambodia was also thrown into turmoil under Pol Pot's brutal Khmer Rouge. More than one million people deemed guilty of crimes against the regime died in the "killing fields" referred to by Mr Bush.
There is likely to be fierce debate over Mr Bush's linking of US withdrawal from the region to the rise of the Khmer Rouge. Some historians argue Pol Pot would never have won power without the US economic and military destabilisation of Cambodia.
But the president's wider point is that the US struggle then - and now in the war on terror - has not fundamentally changed, and that retreat would bring similar chaos to the people of Iraq, and deal a similar blow to US credibility.
"There are many differences between the wars we fought in the Far East and the war on terror we are fighting today," Mr Bush said.
"But one important similarity is that at their core, they are all ideological struggles.
Critics of Mr Bush's handling of the Iraq War have also invoked the US experience in Vietnam. But they have focused on other themes, saying escalating the US military presence in Iraq will only make matters worse.
Observers suggest that the president's latest comments are a "very selective" association of the conflicts.
James Denselow, an Iraq analyst at King's College, London, told the BBC: "This smacks of spin, a last throw of the dice designed to pre-empt the anti-war lobby and justify the US's continued presence.
"This is an issue of how America goes to war, and how it gets out of it. It is rare for a leader in a democracy to take a country into war, and to take the country out."
Mr Denselow argues that the situation in Iraq is more "amorphous" than in Vietnam.
It is a country divided along sectarian lines, he says, but not in the same way that Vietnam was split into North and South when US troops were there.
Fighting in Iraq is also less conventional, he says. The security situation in Baghdad is "already worse".
Analysts say a US withdrawal is more likely to draw in more of Iraq's neighbours. There has already been a large exodus of refugees to the countries surrounding Iraq. There is already chaos in Iraq although it could, of course, get worse.
Vietnam has hitherto been an unwelcome, often-dismissed point of comparison, but is one that is increasingly being made by both opponents and supporters of the war.
The battle now seems to be over who picks the points of comparison, and what lessons they choose to learn.