The Iraq War was a war of choice. Iraq posed no immediate nor distant threat to the UK or British interests.
The often aggressive and unpleasant regime of Saddam Hussein had been successfully contained by a coalition of allies during the 1990s.
And for ordinary Iraqis - not seeking to engage in politics - life was a little worse than it had been (due to sanctions) but it was stable and 'OK'.
The decision of the UK to get involved in the Iraq war was controversial at the time, and over a million marched in London against it.
It was controversial because there was very little in it for the UK, controversial because the justifications for the war quickly unravelled and controversial because British military personnel began to die in a war that was not widely supported by the electorate.
It also provides a relearning of a timeless lesson of war: that conflict is contagious and often uncontainable. All western powers - whether they were involved in the war or not - are still struggling to contain the contagious impact of Iraq.
Islamic extremism a direct product of the Iraq war
The Iraq war continues to scar us today, and none more so than the rise and rise of Islamic extremism. This forms the second lesson from the Iraq war: the end of reasonableness and the rise of extremism.
We like to say that no-one could have predicted the rise of Islamic State, but this brand of extremism has its origins in the political vacuum left in Iraq and the activities of al-Zarqawi who was able to mobilise support against what he described as the occupying coalition powers.
What could not be predicted - perhaps - is the amount of traction these initially very marginal groupings would attract in terms of funding from certain Middle Eastern states, the support they would attract from western youths transiting between the Middle East and Europe who have picked up ways of thinking and military ways of operating that have made them such a threat on the European mainland.
In the response to this growing threat, we have seen western intelligence and security agencies engaging in morally and ethically dubious practices (such as torture and kidnapping / rendition) and dragnet surveillance of entire populations.
Security elites have met the unflinching unreasonableness of jihadists with their own technocratic unreasonableness, some of which has alienated citizens from their governments but all of which has changed the relationship between citizens and their governments.
The refugee blowback has holed the EU below the waterline
The Iraq war - so controversial amongst European Union member states - has come back to fatally undermine the EU. The third lesson from Iraq is 'blowback', the term-coined by the CIA to describe the consequences of military actions.
The radical Islamist groups unleashed by the Iraq war have unsubtlly undermined the European project via insurgent military attacks in London, Madrid, Paris, and Brussels. Those same groups have attracted large numbers of European youths (some estimated 5,000) into the conflicts in Iraq and Syria, which in turn has forced thousands to flee these conflict zones and head for the relative safety of Europe.
Fear of people from alien cultures traumatised by the experience of war has spooked an ever growing number of European citizens, who have turned to populist politicians with readily accessible answers to this 'problem'.
The political mainstream have failed to respond adequately: initially because they thought it was beneath them, and latterly because it is a problem that requires sophisticated responses over a stretched time frame. The blowback from Iraq is the death of the European project.
Who trusts 'experts' now?
The recent Brexit vote provides the fourth lesson: the death of expertise. The Blair government's use and abuse of intelligence product has undermined the public's confidence in expert advice. No longer can the government trot out experts to validate its case.
The trashing of dozens of eminent economists, trade experts, scientists, lawyers, academics by the Leave campaign has its origins in the Blair government's packaging of the Iraq intelligence picture. The public were told to trust intelligence analysts and to do so on faith - not only were these analysts deeply expert, they also had access to information beyond the reach of the public and even most parliamentarians.
It was not the analysis that turned out to be false, but the packaging, but the damage had been done: expertise was no longer to be trusted. Such a change in culture allowed the Leave campaign to undermine the evidence based analysis brought into support the remain side and strongly contributed to the shock decision to Brexit.
It has also seen the end of Blair's social democratic vision of 'third way politics', not just in the UK but across large swathes of the EU: insurgent parties are on the march. It is difficult to see how the political establishment who dominated at the time of the decision to go to war with Iraq re-establishes the trust it needs with the public.
The vital message the Chilcot report will withhold
So, the Chilcot report is likely to criticise Tony Blair and his government. It is likely to say he committed the UK to war earlier than he likes to admit and on a hunch that he could contain the wilder excesses of the Bush Administration.
It is likely to say that defence planners estimated that it would take at least 15 years to return Iraq to stability, and that this has proved to be a conservative estimate, not the wild over-estimate that politicians suggested at the time.
Chilcot is likely to say that intelligence officials warned Blair that the jihadists would bring their war to the streets of the UK and that Blair's judgement was that he should seek to meet them on his terms, aggressively and early.
The Chilcot Inquiry will tell us a lot of what we already know. But it will not tell us that the Iraq war sowed the seeds for the collapse of the European project, for fundamental changes in our political culture and the creation of a world in which it is becoming less safe for Europeans to travel.
But it is these impacts which we are currently feeling today, and are more deserving of our collective attention.