It was the belief of those leaders who participated in the Iraq war that the intervention would serve as a model of noble and far-sighted foreign policy. The establishment of a “free Iraq at the heart of the Middle East”, George W Bush predicted in 2003, would be “a watershed event in the global democratic revolution”. A decade later, Iraq has become a model but one of failure. The state that the Bush administration promised would become “a beacon of freedom, democracy and peace” today ranks as the fifth most at risk of terrorism and as the eighth most corrupt. So inured have we become to the near-daily acts of sectarian violence that the deaths of 150 civilians in this month alone have passed largely without comment.

The arguments advanced for the war are now so discredited that it is easy to forget how widely accepted they were at the time. The invasion had the support of most Labour MPs and, with the notable exception of old-style Tory sceptics such as Kenneth Clarke and Malcolm Rifkind, almost the entire Conservative Parliamentary Party. In the US, 58 per cent of Democratic senators, including Joe Biden, Hillary Clinton and John Kerry, voted to approve the use of force.

In a leader published on 17 February 2003, we argued: “The case made for war must be like the case made for guilt in a court of law: it must be beyond all reasonable doubt. That case has not been made and it has patently failed before the jury of public opinion. Tony Blair should accept the verdict.” Ten years later, we see no reason to revise this judgement. A war fought to prevent the proliferation of weapons of mass destruction, to reduce the threat of terrorism and to protect civilian life achieved the reverse in each case.

It was the decision to disarm Saddam Hussein of his non­existent arsenal of chemical and biological weapons that prompted the other two members of “the axis of evil” – Iran and North Korea – to seek nuclear weapons as the ultimate insurance against pre-emptive attack. As the former US sec­retary of state Madeleine Albright laconically observed, “The message out of Iraq is that if you don’t have nuclear weapons, you get invaded. If you do have nuclear weapons, you don’t get invaded.” There was, contrary to US propaganda, no evidence of any relationship between Iraq and al-Qaeda, at least until the invasion established one. The country became a haven for jihadists and the disastrous occupation the most powerful recruiting sergeant for their cause.

Shortly before the war began, Mr Blair promised MPs that although civilian casualties would undoubtedly occur, Saddam Hussein would be “responsible for many, many more deaths even in one year than we will be in any conflict”. Yet a 2006 study by the Lancet medical journal, the most authoritative survey of post-invasion mortality in Iraq, estimated that nearly 655,000 more Iraqis died than would have been expected had the invasion not taken place. Though many of the deaths were attributable to al-Qaeda and its surrogates, the Lancet found that 186,000 were due to action by coalition forces.

All of this was predictable and predicted but we recognise that many of those on the left who supported the invasion did so in the sincere belief that even war was preferable to the survival of the murderous Ba’athist regime. As John Lloyd (who makes a welcome return to the NS this week) reminds us on page 27, Saddam Hussein was no mere “tinpot dictator” but a sadistic megalomaniac who invaded one of his neighbours (Iran), sought to annex another (Kuwait) and pursued terrifying campaigns of genocide against the Kurds and the marsh Arabs. That the west armed and supported him throughout the 1980s arguably only heightened the responsibility to cancel this moral debt by removing him from power.

But the lesson of the Arab spring, an authentic democratic surge of a kind not envisaged by Mr Bush and Mr Blair, is that regime change need not be synonymous with western military intervention. Tyrants such as Egypt’s Hosni Mubarak and Tunisia’s Zine el-Abidine Ben Ali were toppled from within by popular uprisings.

Those who supported the war argued that there was no reasonable alternative to a US-led invasion. “You go to war with the president you’ve got” was the common refrain. Yet while contending that the end justified the means, the pro-war left failed to recognise that the means change the end. It was foreseeable that an administration populated by small-government Republicans with little interest in state-building would prove unable to create a stable and democratic Iraq. As one of the anti-war playwright David Hare’s characters remarks, “When you knew what sort of butcher was the surgeon, there was no doubt about the outcome of the operation.”

Though the return of free elections in Iraq is no small achievement, it is disingenuous of the war’s supporters to call the country a flourishing democracy. It is not. Iraq has been torn apart by sectarianism; its prime minister, Nouri al-Maliki, a former Shia dissident, is not a Jeffersonian liberal but a sectarian autocrat who, as Adnan Hussein, editor of al-Mada newspaper, writes on page 31, has exploited the country’s young constitution to concentrate ever greater power in his hands.

Ten years on, Iraq, like Suez before it and now Afghanistan, has become a byword for western failure, a permanent warning of the perils of wrong-headed intervention. In the US and the UK, a new generation of centre-left leaders has sought to draw a line under the invasion. Barack Obama, who opposed the intervention, spoke of a “decade of war” coming to an end in his second inaugural address, while Ed Miliband used his first, cathartic speech as Labour leader to denounce the Iraq war as “wrong”.

Chastened by recession, the indebted west has neither the will nor the capability to mount interventions on the scale of Iraq. For that, perhaps, we should be grateful.