Is it just too Blair-hatingly mad to blame Tony Blair for the appalling humanitarian disaster in Aleppo, and the rest of Syria for that matter? A man who has been out of power for a decade and who has spent the last decade or so devoted to finding peace in the Middle East?

You don’t have to believe that Blair was some bloodthirsty lunatic or slavish poodle of George W Bush to see that there are three good reasons to trace the tragedy that has befallen the people of Syria, including the greatest refugee crisis in Europe since the Second World War, right back to Blair’s policies.

First; the rise of Isis. Blair admitted last year that there are "elements of truth" in the theory that the invasion of Iraq, and the mess that followed, helped feed the rise of Isis. That’s good enough for me.

Without rehearsing yet again the arguments that have been thoroughly examined in the Chilcot and the other reports on the 2003 attack on Saddam Hussein, there is little doubt that – whether the war was legal, illegal, morally justified or morally outrageous – it has led us to where we are now. It is difficult to imagine Isis thriving under Saddam. It is hard to imagine it arming and staffing itself with the sizeable remnants of Saddam's army had the US occupiers not decided to disband the old Iraqi army and proceed with “de-ba'athification”.

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The rise of Isis was certainly unpredictable, and took many by surprise – until our correspondent Patrick Cockburn warned the world that this new force of mediaeval barbarism was about to pile more agony on already fractured and wounded nations. No matter; it would very likely not have happened with anything like the ferocity it did were it not seeded in the conditions of chaos in Iraq.

Second: intervention. The mess in Iraq (and Afghanistan, a far more justified and legal intervention than the later one), persuaded public opinion in the West that such interventions are necessarily disastrous and to be avoided at all costs. That was the principal argument used by Labour, for example, in the debates on UK intervention in 2013.

No matter how heart-breaking the stories coming out of Syria were, and no matter how pitiful the flood of refugees, the public was turned off the idea of muscular humanitarian intervention of the kind Blair used to champion. They were not interested in nation saving, nor in nation building. We’d shed enough blood and spent enough money on these futile campaigns. The failure in Iraq taught us a lesson we wouldn’t forget. But that may have been the wrong lesson, for a war in Syria could have been more justified and more legally founded than the invasion of Iraq. That is certainly a possibility.

Aleppo before the Syrian Civil War Show all 12 1 /12 Aleppo before the Syrian Civil War Aleppo before the Syrian Civil War Aleppo before the Syrian Civil War A man crosses a street in Aleppo, December 12, 2009 Reuters Aleppo before the Syrian Civil War Aleppo before the Syrian Civil War A vendor sits inside an antique shop in al-Jdeideh neighbourhood, in the Old City of Aleppo, December 12, 2009 Reuters Aleppo before the Syrian Civil War Aleppo before the Syrian Civil War A view shows part of Aleppo's historic citadel, overlooking Aleppo city, Syria Reuters Aleppo before the Syrian Civil War Aleppo before the Syrian Civil War A view shows part of Aleppo's historic citadel, Syria Reuters Aleppo before the Syrian Civil War Aleppo before the Syrian Civil War Visitors walk inside Aleppo's Umayyad mosque, Syria Reuters Aleppo before the Syrian Civil War Aleppo before the Syrian Civil War People walk inside the Khan al-Shounah market, in the Old City of Aleppo, Syria Reuters Aleppo before the Syrian Civil War Aleppo before the Syrian Civil War A man walks past shops in al-Jdeideh neighbourhood, in the Old City of Aleppo, Syria Reuters Aleppo before the Syrian Civil War Aleppo before the Syrian Civil War People walk along an alley in al-Jdeideh neighbourhood, in the Old City of Aleppo, Syria Reuters Aleppo before the Syrian Civil War Aleppo before the Syrian Civil War Visitors tour Aleppo's historic citadel, Syria December 11, 2009 Reuters Aleppo before the Syrian Civil War Aleppo before the Syrian Civil War A general view shows the Old City of Aleppo as seen from Aleppo's historic citadel, Syria December 11, 2009 Reuters Aleppo before the Syrian Civil War Aleppo before the Syrian Civil War People walk near Aleppo's Bab al-Faraj Clock Tower, Syria October 6, 2010 Reuters Aleppo before the Syrian Civil War Aleppo before the Syrian Civil War A man stands inside Aleppo's historic citadel, overlooking Aleppo city, Syria December 11, 2009 Reuters

It’s true that will never know if a more determined Western action in Syria could have changed the course of the war. There is a perfectly valid counter-case for believing that earlier and stronger intervention by the West, including by the RAF and British forces on the ground, could have done no more than make matters worse, turning yet another Middle Eastern people against us. We might now be in roughly a mirror image position to Russia, grinding the Assad forces and Isis into the ground while the Free Syrian Army and other opposition groups take it out on their enemies.

Or, alternatively, it might have tamed Assad and led to the formation of a stable new regime in the country, one where Isis could in turn be attacked with the will and support of the whole people of Syria. To admit of the possibility is to admit that the Iraq adventure badly warped our judgement for years after.

Third, Blair so alienated our allies in Europe over the Iraq invasion that there was little prospect of them supporting a broad-based international coalition, with the single exception of France. That was part of a wider international failure, focused on the United Nations.

One legacy of Blair and President George W Bush was to leave the UN totally useless in the face of the aggression of the Assad government, Isis, and other extremist groups. For the same reasons that they alienated western public opinion they also undermined international support for a legal intervention in Syria – which would always have been a very difficult diplomatic challenge.

What should have happened is this: the UN would have led a truly international force under an appropriate resolution to bring stability to Syria and isolate the factions fighting for control. Maybe that could never have happened with Russia, Iran, Turkey and Saudi Arabia following their own agendas, but, again, it was at least a possibility if the toxic legacy of Iraq had not poisoned so many relationships.

I am not a Blair-hater, and do not regard him as a war criminal. However I do think, as he himself admits, there were mistakes over Iraq and we have not felt the last of the consequences yet.