Niall Ferguson on the consequences of withdrawing from Iraq....

Withdrawal from Iraq now would turn out to be an incredible bloodbath.

Is it time, then, for the Americans to revive their tried-and-tested policy of proclaiming victory and getting the hell out? I suspect many readers - not least those with sons, brothers or husbands in the services - fervently wish that they would, preferably preceded by us.

And yet, as Kipling so well understood, there are worse things than trying, however imperfectly, to police a foreign land. (Having spent last week in Cambodia, I have just been forcefully reminded of the horrors that befell Indo-China after the Americans abandoned South Vietnam.)

The kind of violence that we could see in Iraq if we quit now, leaving full-scale civil war to rage, would dwarf all that has happened since 2003. I once asked a friend in Beirut what he thought would end up happening in Iraq. "Like Lebanon in the 1980s," he replied, "but to the power of ten."