The Independent on Sunday always knew, if Tony Blair did not, that war has a terrible tendency to go wrong. That is why the bar for resort to military action has to be set very high indeed. This weekend the diabolic consequences of a reckless American reaction to 9/11, invading a country that had nothing to do – at the time – with al-Qa'ida, have been laid bare. The reality that the US military has sought to obscure has now been brought into the open. WikiLeaks presents a damning picture that confirms emphatically what this newspaper, alone among quality Sunday newspapers, has argued all along.

On 16 February 2003, the day after the biggest march this country has ever seen, we said: "The propaganda for war produced by the British and US governments has been laughably amateurish. The attempts by Messrs Bush and Blair to link Iraq with al-Qa'ida have not been convincing. So far the senior UN weapons inspector, Hans Blix, has not come across weapons of mass destruction. Even if he does, The Independent on Sunday would not support war.

"The key question in relation to weapons of mass destruction is whether Saddam would use them in the certain knowledge that such an act would provoke a war that would destroy him. We believe that deterrence still works. These are not lofty questions, but hard-headed and realistic objections to a war with no obvious cause."

Iraq has reaped the whirlwind sown by George Bush's insouciant refusal to consider the eminently knowable unknowns, to adapt the words of Donald Rumsfeld, his Defense Secretary. The deaths of 150,000 Iraqis, the overwhelming majority of them civilians. The killing by US soldiers of unarmed civilians, including children, and of Iraqis trying to surrender. The horrible mundaneness of friendly-fire incidents, including British troops killed by US soldiers because they were listening to their iPods. The turning of a blind eye to abuses by Iraqi security forces. The daily diary of mismanaged sectarian conflict.

None of this is likely to change minds about the case for war in 2003. But it should. Even those who insist that President Bush and Mr Blair acted from noble motives ought to accept that they have no defence against the charge of incompetence. The principal responsibility for the failure to take seriously the Doctrine of Colin Powell, US Secretary of State, "You break it, you own it", lies with President Bush and the Pentagon. Mr Rumsfeld and his deputy, Paul Wolfowitz, were negligently dismissive of warnings of a power vacuum, sectarian strife and a breakdown of civil order. The number of US troops deployed was insufficient to prevent looting from the start. And the country still does not have a government, after the elections seven months ago.

But Mr Blair was warned too. This newspaper broke the story of his meeting in November 2002 with six academic specialists in Iraq, including Sir Lawrence Freedman and Professor George Joffe, who told him that occupying the country would be difficult at best and catastrophic at worst. One of those present told us: "I was staggered at Blair's apparent naivety, at his inability to engage with the complexities."

It was not the ignorance so much as the lack of curiosity that was so reprehensible; the wilful, casual, reckless refusal to consider the practicalities of running a country of 25 million people once the totalitarian lid on the pressure cooker was prised off.

Mr Blair continues to evade responsibility for this error of judgement. In his memoir, published last month, he claims that "the issue of the Sunni minority suddenly turned from rulers to ruled was extensively canvassed". But he suggests the real problem was that al-Qa'ida and Iran moved into the country after the invasion, intent on fighting the US and its allies, and that this could not have been foreseen.

All parts of his analysis are wrong. Sunni-Shia tension was a known problem; the Americans failed to anticipate it. Jihadist ideologues and Iranian agents exploited it; and Messrs Bush and Blair had been repeatedly and explicitly warned that they would.

The Iraq war logs constitute a 400,000-page indictment in the court of history for one of the worst judgements in American foreign policy, in which Mr Blair finally faces an unanswerable charge of aiding and abetting. For what it is worth, when so many have suffered and died, those who marched, stood or spoke against the war have been vindicated.