Five years ago a youthful US army general, with a PhD in international relations and a name that seemed plucked from Herodotus, led the 101st Airborne Division into Mosul in northern Iraq. He had taken part in a stunning military victory, but failed conspicuously to celebrate. “This is a race to win the hearts and minds of the Iraqi people,” he said. “And there are other people in this race. In some cases, they want to kill us.”

General David Petraeus is still not celebrating. But he is leaving Iraq in a state no sober observer would have forecast when he took command of US forces there early last year. He has pacified large parts of a country that had descended into a solar-heated hell of suicide bombings and sectarian carnage. He has salvaged some pride for the US military after Abu Ghraib, and seen himself hailed as America's most trusted and talented commander of the past four decades.

The troop “surge” for which General Petraeus is often credited was in fact the idea of his second-in-command. But he approved it, secured backing for it in Washington and made it work. Crucially, he also co-opted the very Sunni militias that had sabotaged four years of allied reconstruction efforts, and deployed them as a new and deadly vanguard against al-Qaeda.

The scholar-warrior from Princeton and West Point now turns his attention to Afghanistan. Physically, he will move from the green zone in Baghdad to Centcom HQ in Florida. But his prodigious energies will be devoted to defeating the Taleban where Nato and his own predecessors have failed so far. To succeed, he will have to defy history. His record suggests he is the man to do just that.