In the initial aftermath of the attacks, the European Union rallied in support of its transatlantic ally, anxious to show solidarity and unity.

But the solidarity and the internal cohesion did not endure. The unity proved to be only skin-deep and the EU came to regret some of its hasty and badly calibrated responses.

At root, the cause of the EU’s difficulties was that it let its response be guided by the administration of president George W. Bush.

The attacks on New York and Washington – and later on Madrid and London – called for greater international co-operation on many levels to combat the terrorist threat. But technical co-operation, such as the tracking of terrorist finances, was not at the heart of the response to 9/11.

That response was, primarily, 19th-century military action against a new kind of threat: transnational non-state terrorism. The limitations of that approach were compounded by the spuriousness of Bush’s decision to invade Iraq.

The emotional scars from the political divisions at that time in Europe are still livid. Those divisions had policy consequences that still linger. The EU’s foreign and security policy was set back badly by the painful fall-out between France and Britain over Iraq. Franco-British co-operation is a necessary condition for a stronger EU defence; it is only now that such co-operation is being reassembled following the bitter clashes between Tony Blair and Jacques Chirac in 2002-03.

The US continued its crusade against an “axis of evil” into war with Afghanistan, carrying with it – to varying degrees – its European allies in “a coalition of the willing”. That conflict, now entering its second decade, has demonstrated Europe’s lack of preparedness for military operations, but European voters have been less concerned about this embarrassment than they might have been, because mostly they have regarded the campaign as the US’s war, not Europe’s.

Not everything, however, can be laid at the door of the Americans. While the decision of the Bush administration to attack Iraq, for reasons now evidently unconnected with the attacks of 9/11, damaged the ‘European project’, the EU has itself to blame for its subsequent inability to balance security with liberty.

Such a balance is still elusive, as the recent battles over sharing with the US bank transfer data and passenger name records illustrate.

Most emblematic, perhaps, is the history of the European arrest warrant. In the wake of 9/11, the European Commission wrapped up two years of drafting with record speed: on 19 September 2001, it adopted a proposal for a European arrest warrant, which was positively received by national interior ministers on 20 September during an emergency meeting, and by a special European Council the following day. What had been a highly contentious piece of legislation, opposed by many member states, was recast as an important tool in fighting terrorism.

Since then, the implementation by national authorities of the arrest warrant has been inconsistent, indeed abusive. Its very premise – that EU legal systems provide comparable safeguards of due process – is deeply flawed. European anti-terrorism officials have gained powers over innocent citizens that would have been unthinkable before the events of ten years ago; today, they barely warrant a shrug.

With the perspective of ten years, it is possible to see that, by allowing Bush to set the “axis of evil” agenda, the EU shirked its responsibility to develop a nuanced response to the threat of home-grown terrorism. The Bush rhetoric portrayed the terrorists as an external, existential threat. The truth was more complicated and the EU should have been more alive to the subtleties, especially since terrorism was not new to Europe, even if aspects of the al-Qaeda terrorism were different.

On the occasion of the tenth anniversary of the attack on the Twin Towers, it is right that the EU mourn the victims of terrorism and salute the courage of those who work for its security. But it should also reflect on its policy mistakes.