It is now clear, as indeed it was in 2003, that most people have no wish to embroil Britain militarily in the Middle East.
Thursday's vote by MPs to bar the way to British involvement in a war against Syria is a vindication of the mass anti-war movement in this country over the last decade.
Parliamentarians of all parties claimed that they had "learned the lessons of Iraq". Better late than never, of course.
But the millions who protested against the Bush-Blair aggression in 2003 understood the lessons at the time.
After hundreds of thousands of dead in the intervening years, their message has reached the green benches: there is hardly a problem in the Middle East (or elsewhere) that Anglo-US military intervention cannot make worse.
This is the case in Syria, too, where the crying need is not for more bombing by anybody, but for a concerted drive for a Syrian-based political solution.
The starting points have to include the west abandoning its cynical policy of basically prolonging a civil war which it wants neither side to win.
The seeds of Cameron's defeat were sown in February 2003, when about 2 million people marched against the Iraq war, only to have Tony Blair ignore them.
That democratic outrage has hung over British politics as a cloud ever since and has, along with MPs expenses and the failures of neoliberalism but more serious than either, condemned politicians to the pillory of public disdain.
The Commons vote is more than a humiliation for the prime minister, who urged Obama towards action in Syria only to find he could not carry his party or his country with him.
It is also a rebuke for all those in the political class who have taken the view that foreign policy is an elite issue, in which ordinary people have no interest and should have no say.
It is now clear, as indeed it was in 2003, that most people have no wish to embroil Britain militarily in the Middle East, that they want the government to abide by international law and the authority of the UN, and that standing "shoulder to shoulder" with the US come what may has no purchase on their views or feelings.
The "special relationship" and "liberal interventionism" have alike been exposed as preoccupations of the establishment – indeed, only a section of it now – with no democratic mandate underpinning them.
The possibility is now open for Britain playing a different role in the world, breaking with the policies and preoccupations of imperialism.
That change is nothing like secured yet.
Only two years ago there was cross-party support for intervention in Libya's civil conflict, an intervention that, in terms of delivering a stable and democratic country, has scarcely worked better than the wars in Iraq and Afghanistan.
There will be continuing pressure to deploy the military to secure big-power ends across the region.
But a corner has been turned, and the sustained mass pressure of the anti-war movement, which as conservative columnist Peter Oborne has remarked, has "shown more mature judgement on these great issues of war and peace" than those in power has undoubtedly been a decisive factor.
Ed Miliband deserves a measure of credit too, of course. As a byproduct of his support for international law on this occasion, he has got his leadership back on the front foot.
It will have escaped nobody's notice that, as with the Murdoch phone-hacking scandal, he does best when he most obviously distances himself from the toxic legacies of Tony Blair.
Blair himself cuts a bizarre figure – the "Middle East peace envoy" who urges war in the region on every conceivable occasion, as he bobs around the Mediterranean on an oligarch's yacht. He has been called many things, but today at last we can deliver the most damning judgment of all. He is the past.
Source: The Guardian