It was the day that shook the world. From cold, grey, sub-zero London to sunny Sydney, a vast tide of humanity marched in every continent in the most momentous display of mass solidarity ever seen, hoping to stop the impending US-led invasion of Iraq.
The New York Times talked of the day showing two superpowers on the planet - the USA and world public opinion. The global hurricane provoked political turmoil worldwide and Labour Prime Minister Tony Blair's biggest political crisis.
In an estimated 600 cities across the world, people marched - possibly more than 30 million in total - against a threatened war which they rightly feared would lead to greater global instability.
Ten years on from 15 February 2003, all the fears of the marchers have come to pass and then some. The invasion led to the slaughter of more than half a millionIraqis. Millions more Iraqis have been displaced from their homes. Thousands of service personnel - including 4,486 in the US and 179 in the UK - have died.
Around the world lives continue to be lost and damaged in the name of the 'war on terror'. For example through drone strikes in Afghanistan and Pakistan, and the latest onslaught on Mali; through genocidal slaughter and repression, as in Sri Lanka; and through increasing denial of democratic rights. These are, in reality, wars conducted in the interests of big business.
The war for oil has left Iraq and the world in a state of permanent instability to this day and hasn't done anything to reduce the risk of terrorism.
The scale of opposition to Bush and Blair's drive for regime change in Iraq could not be doubted after that momentous day. Up to two million marched in London. Demonstrations took place in most major cities across the USA and there were huge demonstrations in every country where their "leaders" backed Bush's war drive.
However, the protests of the biggest anti-war opposition humankind had ever experienced did not succeed. The war went ahead with all its ultimate consequences. So does that mean that the tens of millions of us who marched failed or that demonstrations change nothing?
Undoubtedly, the demonstrations made the ruling classes of the world pause, seeking further justification in the form of a second UN resolution for their imperialist aggression.
Socialists explained that the UN process was "merely a diplomatic ploy to legitimise a predetermined decision to launch a war against Iraq" and that the UN was unlikely to act against the interests of its most powerful constituent, US imperialism.
Moreover, the scale of opposition in Britain saw Blair, previously known as 'Teflon Tony' because apparently no scandal or complaint could stick to him, teetering on the brink of defeat. The impact of the anti-war movement was something from which he never recovered.
The millions marching on that day were not marching to defend Saddam - as some, such as Observer columnist Nick Cohen, claimed. Most who marched were fully aware that Saddam was a vicious dictator who had ruled through the most brutal repression. The Socialist Party also gave no support to Saddam's rule and argued that his overthrow was the task of the Iraqi people.
No one doubted that Saddam had used chemical weapons in the past and could use them again - though there was enormous scepticism even then about the claims of stockpiles of so-called weapons of mass destruction, which were later proved bogus.
The main reason millions marched, and hundreds of millions more backed the marchers, was because they didn't believe foreign intervention was justified. They feared the consequences; and they suspected that, behind the propaganda fig leaves of George W Bush and Blair, this was a naked imperialist war for regime change to get their hands on Iraq's oil. It was also concerned with US imperialism's strategic interests and Bush's prestige after the 9/11 attack.
The millions came from all sections of society. There were those from socialist organisations and trade unions, and those who had been involved in the anti-globalisation movement in the decade previously, who knew what the likely consequences of war would be.
Yet, overwhelmingly the millions were people who had not previously been involved in political activity and who were not persuaded of the need for war in Iraq and were motivated to take action themselves.
The demonstrations - particularly in Britain - represented a unique chance for those leading the movement to clearly call on those newly mobilised masses to come behind a new political movement: a movement that could offer an alternative to the neoliberalism and war offered by establishment politicians.
The demonstration speakers represented a kaleidoscope of British society - reflecting the Stop the War Coalition's (STWC) 'popular front' approach.
This meant that, despite objections from the Socialist Party, the leadership of the STWC, strongly influenced by the Socialist Workers Party (SWP), bulldozed the decision through the STWC steering committee to allow a platform to then Lib Dem leader Charles Kennedy - without any public criticisms of the fact the Lib Dems only opposed the war without a UN mandate.
The leadership also refused to allow any speaker directly on behalf of a socialist organisation, denying the millions who marched a chance to hear a real alternative to war and capitalism. This undoubtedly helped to build up the Lib Dems' 'radical' image particularly among young people, helping to pave the way for the Con-Dem coalition.
Former Labour cabinet member Mo Mowlam, who was also to speak, was being promoted by STWC leaders as a Labour rebel, but six weeks later she called in the Daily Mirror for more bombing to win the war.
The Socialist Party explained in leaflets and articles that, "unless Blair's rule, and the interests of the capitalist ruling class that he represents, are put at greater risk from a movement at home than they would be by not going to war, Blair will not be deflected from his path".
We explained that this meant action before the invasion took place, as well as after; building on the magnificent turnout on 15 February with mass civil disobedience, especially strike action, and seizing the time to build a mass political alternative, preferably in the form of a new mass workers' party.
Among the platform speakers at the demo were some trade union leaders who made the call for industrial action to stop the war, who were also uneasy about giving a platform to Liberals and Labour. In its material and speeches elsewhere, the Socialist Party supported this but argued that decisive industrial action to stop the war would require serious preparation.
Former Labour MP George Galloway had said in private discussions before the big day that he was going to use his speech to call for a new anti-war political alternative to be established. On the day he pulled back and spoke more obliquely, denouncing Blair and Bush, but only warning in general of splits in the Labour Party if Blair went ahead in supporting the war, saying that he and others would "refound the Labour Party" on socialist principles.
In the event George Galloway was expelled from the Labour Party in October 2003, at the time of Blair's choosing, and that opportunity to launch a mass party was lost.
However, even though some punches may have been pulled in speeches, why did the demo not then translate into mass civil disobedience and general strikes which could have halted Britain's involvement in the war?
The steering committee of the STWC met three days after the massive demonstration. The SWP and Communist Party of Britain leadership of the STWC acknowledged that "there is a massive responsibility on this committee to come out with a clear plan of action in the next few days."
At the time, the Socialist Party had three members on the 50-plus steering committee but did not have any members in the inner core of officers who made the day-to-day decisions and who were responsible for the political direction of the STWC.
However, it was forcefully put by Socialist Party members at the meeting that it required something more than abstract talk of a "political crisis" to make "mass civil disobedience" and effective industrial action a reality.
Under pressure from us, backed up by former NUM leader Arthur Scargill and George Galloway MP, it was agreed that "after getting two million on the streets we need to take up the call made by some trade union leaders for a reconvened TUC and to popularise the idea of all forms of industrial action."
It was understood at that meeting that it would be wrong to put all our faith in a reconvened TUC calling industrial action, as was proved a few weeks later.
After 15 February, a serious attempt was needed to involve the majority of those who had marched into representative, democratic and effective coalitions at every level of society.
Socialist Party members were also particularly vocal on the need to draw on the experience of a mass civil disobedience movement that had brought down Thatcher - the anti-poll tax movement where mass demonstrations were combined with 18 million people refusing to pay the hated tax.
Of course, a campaign to stop a global war was on a bigger scale than the anti-poll tax movement, but the scale of opposition and potential anger that could be mobilised was even greater as well.
But, we argued, the most crucial aspect of building a movement out of the mass turnout on 15 February had to be organising effective and sustained action in the workplaces. Strikes, then as now, show that it is working class people who have the real power in society to bring everything to a halt.
To bring to reality the slogan of "stop work to stop the war" serious preparations had to be made. Socialist Party member Bernard Roome, who was a member of the Communication Workers Union national executive at the time, had successfully moved a resolution at the union's executive "to campaign for all members to take protest action on the day that war is officially declared."
Socialist Party councillor and former Labour MP Dave Nellist also had successfully moved at a STWC steering committee that a planning meeting calling together all the executive and leading activist members of trade unions should be convened to coordinate action on Day X - the first day of the war.
Even before Day X, if a mass day of civil disobedience had been called on the day that Parliament voted to support an invasion, then it was possible this could have had the impact to force MPs to vote against war and defeat Blair.
If Britain's participation in the invasion of Iraq had been stopped, even at that late stage, this would not have stopped Bush and the US regime. It was a life or death matter for the regime in the US.
In fact, veteran journalist Bob Woodward, in his book Plan of Attack, revealed that in March 2003 Bush had offered Blair the chance to keep British troops out of the war. But Blair was determined to assert Britain's prestige.
However, the growing anti-war movement in the US would have been given an enormous push from the defeat of Blair and an impetus could have developed for a new political party in Britain.
Blair and much of the Labour leadership faced growing anger over their war policies, as well as pursuance of privatisation, university fees and their anti-working class agenda. This even spread to the party itself with a parliamentary 'revolt' and a handful of resignations.
Could Labour have been reclaimed for the anti-war masses, starting to take action and thinking about how to effect change? Following years of erosion of Labour's democratic structures it was impossible for working class people to have an impact on the party's policies, as was shown by various failed attempts to pass anti-war resolutions.
Even those who argued reclamation was possible put forward no clear strategy beyond asking people to join, an invitation that most anti-war activists declined and membership and support fell.
The Socialist Party argued that the anti-war movement did need a political voice and welcomed all positive steps towards working class political representation. However, in the belated formation of Respect, George Galloway, the SWP and others made fundamental programmatic and organisational mistakes, which prevented Respect from providing an effective political channel to the masses moving into action against the war and over other issues.
After 15 February, there were inspiring displays of trade union action, civil disobedience and the heroic organised and determined action of school students who walked out en masse on Day X - the day the war started.
International Socialist Resistance, a youth campaign initiated by young Socialist Party members, had distributed 60,000 leaflets on 15 February making a call for school students to organise themselves and prepare for school strikes. ISR members helped coordinate the strikes in many areas.
However, the leadership of the anti-war movement did not seriously address how to build and sustain a mass campaign of civil disobedience against the war.
Instead, they organised cross-party People's Assemblies and further demonstrations. Feeling the hot breath of the anti-war movement on their backs a number of politicians from the pro-war parties found their 'consciences' and participated. But the STWC leadership did everything they could to accommodate these right-wing establishment representatives - rather than make demands on them.
The scale of the anti-war movement in Britain, the US and elsewhere did lead to on-going crises for Bush and Blair, but not enough to topple either regime and stop the war.
Ten years on, the consequences of this blood for oil reverberate everywhere still. Nowhere is this more the case than in Iraq - billions of dollars were poured in to try and rebuild the country's infrastructure but whole swathes of the population have very limited access to electricity and drinking water.
Meanwhile the profits of the subcontracting and arms companies have skyrocketed. Deadly and near-daily attacks on security forces and civilians continue to claim lives.
15 February 2003 was an inspiring day to be alive, you saw the potential for the war to be stopped. Nevertheless, it also showed that mass demonstrations are not enough in themselves to stop political leaders whose power, prestige and ultimately political survival are at stake.