I supported regime change in Iraq, voted for the war and argued for it all over the media. But America and the EU now need to learn the lessons of the way that we went to war, so that we may build a new internationalism.
As a new Labour MP, I came to parliament seeing no contradiction between being pro-European and pro-American. Then, in the months after the 11 September attacks, I watched in horror as Europe and the US fell out. When America developed a new foreign policy in response to al-Qaeda's attacks, Europe's response was distrust verging on contempt. Instead, we could have seen it as an opportunity. Europe could have welcomed an America committed to the spread of democracy. After all, that is exactly what the EU has been doing since its creation. It is also what Woodrow Wilson was after when he said he wanted the First World War to make the world "safe for democracy".
By being so hostile to the US, European countries seemed to be positioning themselves against the goal rather than questioning the means and the tactics. And that contributed to America's mistake, which was to allow the break-up of the global coalition that arose from 9/11.
Tony Blair agreed that we needed to deal with Saddam Hussein - but he thought that this should be backed up by international consensus. He tried everything to get that support reaffirmed through a second resolution. Had he succeeded, our subsequent actions would have been less difficult. I don't just mean that the reconstruction of Iraq would have been easier, although our relative success to date in Afghanistan is at least prima facie evidence that it would. I mean that military action against Iraq, with unambiguous international support, would have changed the incentives of the 40 or so dictators around the world. They would have known that persistent defiance of UN resolutions, such as murdering civilians or sponsoring terrorism, would not be tolerated.
It is not too late. With the spread of democracy we have not just a goal - we have also our best tool. No democracy has ever started a war against another. No democracy sponsors terrorism or allows famines to develop. This new internationalism would combine the traditional internationalist goals of democratic nations operating in a multilateral order, with the new opportunity of backing that multilateral order up with the Atlantic powers' military and economic strengths.
Why would the US swap unipolar dominance for multilateral ties? Because its relative dominance is only temporary. China and India together account for a third of the world's population: now that economic growth in these countries is gathering pace, political power will no doubt follow. We should use these years of unipolar American power to build a world of multilateral shared power.
Europeans and Americans have much in common. Economically, we're all capitalists. Politically, we're all democrats. Culturally, we share much.
What should we do to prepare for the coming multilateral order? We should take UN reform seriously. Britain is arguing for five new permanent members and four new "rotating" members of the Security Council. The general consensus is that reform of the Security Council's composition is impossible in the short term - but perhaps it is inevitable in the long term. The US, France and Britain should be brave on reform now when it would generate more goodwill because we hadn't been forced to concede it, and when we would have significant influence over the direction of change.
International bodies such as the World Trade Organisation or the International Criminal Court will wield a growing influence on Britain's national interest. We will be in a better position to influence them through the EU rather than arguing by ourselves (and between ourselves). In the European Union we may be inventing an institution that is better suited to the new multilateral order than other, looser, regional groupings around the world.
The potential of the EU underlines the need to make it more effective. We Europeans need to modernise our armies and our economies. We need to heal the old Europe/new Europe rift and deploy our soft power more robustly. The promise of trade agreements can have a real effect on our non-EU neighbours. We need to harness those non-military forms of influence to the goals of democracy and human rights, using them as carrots but also as sticks - for example, being prepared to rescind trade deals when a country is heading in the wrong direction.
I would encourage two policies for the US. The first is to embrace European integration enthusiastically. If it is right that Europe and the US share a fundamental interest in building a multilateral world, then that goal will be better achieved by a strong, united Europe. Second, large coalitions of the slightly annoyed work better than thin coalitions of the willing. Unilateral action may be easier but it carries costs. Between summer 2002 and May 2003, the proportion of Germans with a positive view of America fell by a quarter. In Turkey, which we should soon put on track to join the EU, a third of the population believes that suicide bombing against foreigners in Iraq is acceptable.
We need a regular forum involving the US, the main EU countries and the European Commission. We could reform Nato to provide this or we could create a new body. Discussions of substance could allow us to resolve or compromise any differences and avoid the grandstanding at the UN that characterised the run-up to the Iraq war.
James Purnell is Labour MP for Stalybridge and Hyde