The recent request by the senior US military commander in Afghanistan for more troops has provoked the question of whether Afghanistan could be Barack Obama's Vietnam. There are certainly difficult issues for the Western nations that have troops in Afghanistan, but there is really no analogy with the American role in Vietnam during the 1960s and early 70s.
The most important difference between the two conflicts is that the so-called war in Afghanistan is not a war in any conventional sense.
This might, no doubt, strike the troops under fire there as a matter of semantics, but they are really engaged in a police action against the Taliban, a group of insurgents whose support is confined to some regions of thecountry.
In the 60s, in contrast, the US was essentially confronted by another nation - North Vietnam - that had substantial support from the Soviet Union and China. It is true that there was a huge disparity between the two combatants but the Americans were fighting within political limitations that meant they could never fully use the formidable firepower at their disposal.
This was what a number of international figures, including France's Charles de Gaulle, tried to explain to the US at the time: that while it was infinitely more powerful than North Vietnam, it could not win the war by the means with which it was compelled to fight it.
Another significant difference between the two conflicts is the scale of casualties. It needs to be remembered that in the decade from 1965, almost 55,000 Americans were killed in Vietnam, more than 5000 a year on average. The total loss of life among Americans and their NATO allies in Afghanistan over eight years is less than 1500 (including 12 Australians).
These casualties should not be minimised, of course, but they are obviously small in comparison with Vietnam, let alone earlier conflicts. It is worth remembering that on the first day of the Somme - July 1, 1916 - the British casualties were 60,000, including 20,000 dead.
In the absence of significant casualties it is hard to imagine events in Afghanistan producing the kind of public reaction that occurred in the US in the late 60s, when it became clear that the Vietnam War was not only costing a large number of lives but was being lost. It is probably true that there is little enthusiasm for the conflict among the populations of Western countries that have made contributions to Afghanistan, but strong opposition in these communities does not appear to be widespread. In addition, the main political parties in most of these countries, including Australia, support the present level of military intervention.
There needs to be some realism about Western objectives in Afghanistan. It was never going to be possible to convert this country, which has historically no experience of social democracy, into a Central Asian version of Norway or Sweden.
However, it could hardly be argued that the Taliban would be better for the Afghan people than their present regime. So, if preventing the Taliban from resuming power is one consequence of the presence of foreign troops, that is a good thing.
But it needs to be acknowledged that the real reason for the presence of those troops is an essentially selfish one on the part of America and its allies, including Australia. The aim of the exercise is to prevent Afghanistan being used by al-Qa'ida and other terrorist groups as a base and training camp for attacks on the West.
It is true that there are other countries in the Middle East, Central Asia and North Africa where terrorists are harboured. But Afghanistan and its neighbour Pakistan have been in the forefront of these danger zones. The government of Pakistan has made some progress in dealing with terrorists inside its borders, but this is a task beyond the resources of any Afghan government at present.
What this means, of course, is that there is no immediate end in sight for the Western forces in Afghanistan.
The attacks on New York, London and Madrid during this decade demonstrate the existence of terrorist groups dedicated to the destruction of the West.
One consequence of that - and there are many others as well - is the continued presence of the Americans and their allies in Afghanistan, possibly for quite some years to come.