In the long-running debate about the size and duration of America's troop deployment in Iraq, American and Iraqi politicians have failed to notice that the long-expected withdrawal has already begun.

According to the Pentagon, there are now 145,000 American troops in Iraq, down from 170,000 at the peak of the “surge” ordered by President Bush last year.

As the security situation improves, so the US forces will continue to shrink. Lieutenant-General James Dubik, who is in charge of training Iraqi soldiers, predicted that “security operations” by US ground troops would be finished by the middle of next year. He expects Iraqi forces to take over security across the country's 18 provinces by the end of 2008. Anbar province, once the most volatile, is due to be handed over to Iraqi control this month.

The drawdown has been eclipsed by the politically charged debate in America and Iraq over the future US role in the country. Barack Obama, the Democratic candidate for president, has pledged to withdraw US forces within 16 months of coming to office. Senator John McCain, the Republican nominee, has vowed to keep the forces for “100 years” if necessary. A similar debate is taking place in Iraq, where regional elections are supposed to take place in October. In an effort to win support from key Shia Muslim brethren, Nouri al-Maliki, the Iraqi Prime Minister, has called for a timetable for a US withdrawal as part of a new status of forces agreement with America.

The discussion has only been made possible by the security improvements across Iraq, where by every measure, violence is diminishing and the country is growing more stable.

The change is already having a dramatic effect. Baghdad has announced plans to boost the country's oil industry with the help of Western companies. In the Arab world, countries that once shunned Iraq are now lining up to re-establish diplomatic relations.

Only a fool would be bold enough to predict that Iraq's problems are over. The country faces enormous challenges as it overcomes five years of bloodshed, a shattered infrastructure and the legacy of a sectarian conflict that very nearly pushed Iraq into an all-out civil war.

Those dangers are still very real. Yesterday some 17 Iraqi civilians were killed in shootings and bombings across the country. Al-Qaeda in Iraq may have suffered a heavy defeat but the movement is still active in Mosul and other Iraqi cities. For now, Iraq's neighbours, in particular Iran and Syria, appear to have reined-in support for militant groups, but the move is reversible.

The 560,000 Iraqi soldiers, police and other units have demonstrated that they can restore order in places such as Basra and Baghdad. But Iraq still has no air force, not much of a navy, and when the situation goes wrong they still rely heavily on US military support. Five years after the US-led invasion, the period of American military control over Iraq may finally be coming to an end. But a sizeable force of US trainers, advisers, pilots and other military experts are likely to be needed for years to come as the country struggles to get back on its feet.

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