During the Cold War, NATO survived several "crises". In 1966, France withdrew from the Alliance's integrated military structure. In 1979, the Allies were divided over how to respond to the Soviet invasion of Afghanistan. In the early 1980s, deployment of intermediate-range nuclear missiles in Europe intensified transatlantic tensions. Today, the Alliance faces the first crisis of the post-Cold War era - a crisis brought on by the 11 September terrorist attacks on the United States.

The earlier events were essentially crises of confidence in the Alliance. Today's is a crisis of confidence and capabilities. The United States did not have sufficient confidence in the Alliance to give it a major role in response to the terrorist attacks, even though the Allies decided immediately to invoke Article 5, the collective-defence provision, of the Washington Treaty. The European Allies, in spite of the United Kingdom's involvement in Afghan operations and offers of assistance from many others, did not have the capabilities to make a serious contribution to the high-tech, high-altitude bombing campaign that the United States used to help defeat the Taliban regime in Afghanistan.

How the Alliance recovers from the perception of irrelevance that has grown since the terrorist attacks of 11 September will depend on responses to two questions. The first is whether or not the United States is willing and able to lead the Allies toward further adaptation of NATO's mission to make it more relevant to the terrorist challenge. The second is whether the European Allies recognise the need for such an adaptation and put up the resources to improve their ability to contribute to future counter-terror operations.

Although NATO's invocation of Article 5 was appreciated in Washington, the United States decided to conduct military operations itself and not to seek to use NATO's integrated command structure. Had the United States asked to use NATO's integrated command structure, such a request would likely have created serious political dilemmas for many Allies. The discussion of NATO's area of operation had basically been put aside since the debates leading up to the 1999 Strategic Concept, the document setting out the Alliance's strategy for addressing security challenges, and there was no enthusiasm for re-opening the issue in the middle of this crisis. Furthermore, the United States obviously preferred to keep tight control of any military operations.

Nonetheless, NATO was asked to provide a number of services on behalf of the war against terrorism. On 4 October, NATO Allies agreed to enhance bilateral and NATO intelligence sharing, assist Allies that face terrorist threats because of the counter-terror campaign, grant blanket overflight clearances for US and other Allied aircraft involved in counter-terror operations, and make airfields and ports available to support operations against terror. In addition, the North Atlantic Council agreed that the Alliance deploy elements of its Standing Naval Forces to the Eastern Mediterranean in order to provide a NATO presence and demonstrate resolve. On 8 October, NATO announced that Allied AWACS aircraft would be deployed to the United States to help patrol US airspace. The move freed up US assets for use in the air war against Taliban forces in Afghanistan - the first time NATO assets had been used in direct support of the continental United States.

NATO's response was applauded and appreciated by US officials. Two months after the attacks, US Ambassador to NATO Nicholas Burns argued in the International Herald Tribune that NATO had responded strongly to the terrorist challenge, and that the response demonstrated NATO's continuing relevance. "With the battle against terrorism now engaged, it is difficult to imagine a future without the Alliance at the core of efforts to defend our civilisation," he concluded.

The terrorist attack and the actions required to respond militarily demonstrated in many ways the wisdom of the adaptation of the Alliance that had been underway since the early 1990s. NATO never abandoned the critical Article 5 commitment, but began preparing for the new kind of security challenges Alliance members thought were likely in the 21st century. The implications for force structure were clear: NATO needed more forces capable of being moved quickly to conflicts beyond national borders and prepared to fight in a variety of topographic and climatic conditions using a mix of conventional and high-tech weaponry.

Even though the 11 September attacks constituted a case for invocation of Article 5, the response required the kinds of forces and philosophies that the Allies had been seeking to develop for so-called "non-Article 5 contingencies". NATO formally acknowledged this reality in December when Allied defence ministers observed that NATO, through the Defence Capabilities Initiative, had improved its ability to respond to terrorism, but that "...a great deal more needs to be done... particularly in the areas of survivability; deployability; combat identification; and intelligence, surveillance, and target acquisition...."

Preparing for and conducting operations in Afghanistan, the US administration sought help from the Allies mainly through bilateral channels. In the weeks following the attacks, some Pentagon officials privately dismissed NATO's formal invocation of theprovision and complained that the Alliance was not relevant to the new challenges posed by the counter-terror campaign. Alliance's mutual defence provision and complained that the Alliance was not relevant to the new challenges posed by the counter-terror campaign. Meanwhile, some NATO Allies were led to believe that the United States did not value or want contributions that they might make in the battle against terrorism. Although many Allies, including Germany, pledged forces to the counter-terrorist campaign, these important national contributions did not produce any direct role for the Alliance in the affair.

NATO's initial reaction therefore left many questions unanswered about the future of the Allied response to the terrorist challenge and to the other issues that remained on the Alliance platter. Would NATO countries follow up their Article 5 commitment with resources that would be helpful in the conduct of a far-reaching and long-running campaign against international terrorism? Would the NATO cooperative framework prove helpful or would the United States see it as inappropriate and unhelpful for the kinds of operations required by the war on terror? How would the new framework created by the terrorist attacks and their aftermath affect other key issues for the Alliance, including NATO's future role in the Balkans, coordination of US, Allied and NATO approaches to ballistic missile defence, relations with Russia, continuation of the enlargement process, and future development of the Common European Security and Defence Policy?

Few would question how important it will be to ensure that the members of the Atlantic Community stay united and strong against the insidious threat of terrorism which struck at America's heart on 11 September, and which will strike again if given the opportunity to do so. NATO's initial response to the attacks was impressive and appropriate, but may also reflect some limitations of the Alliance that will influence its future role.

First, it is obvious that the Allies must conduct a "war" against terrorism in ways that deal effectively with terrorist threats while not undermining fundamental democratic liberties or the potential for future cooperation among Alliance members. The Alliance, after all, would lose much of its meaning if it sacrificed the commitment to the values articulated in the Washington Treaty. The extreme nature of the attacks and the threat of more horrors to come have so far helped surmount domestic resistance to counter-terrorist measures. However, each NATO country has its own approach to protecting individual liberties and, down the road, the enhanced intrusion of intelligence and security services in the daily lives of citizens in NATO countries could become a source of friction and controversy.

In addition, most observers of transatlantic security issues remember the debates in the 1990s in which the United States imagined a NATO mandate without artificial geographic limitations, while many European countries wanted to prevent the appearance of an "open-ended" role for the Alliance in dealing with future security challenges. The 11 September events demonstrated that the United States had been right concerning the nature of future threats to transatlantic security, namely that most of them have roots outside Europe and must be dealt with well beyond NATO's borders.

However, the differing perspectives among NATO members concerning the best instruments to employ against disparate threats have not disappeared. They are based on fundamentally different historical experiences, political and military traditions, and available power and military capabilities. France and the United Kingdom have force projection philosophies and global strategic perspectives. But Germany's concepts and perspectives will continue to inhibit the Federal Republic's military role beyond its borders, in spite of the dramatic progress Berlin has made in breaking out of outdated constraints on the use of its forces since the end of the Cold War. Differing roles and perceptions will, on occasion, complicate both consensus formation and cooperation.

In the aftermath of the terrorist attacks, Charles Grant of the London-based Center for European Reform wrote in The Independent that the US choice not to use NATO to run the military operations against terrorist targets in Afghanistan meant that: "It's unlikely the Americans will ever again wish to use NATO to manage a major shooting war." This judgement may or may not be accurate. Washington presumably did not ask that NATO run the military actions in Afghanistan because it did not want to repeat the Kosovo experience, where US management of the conflict was complicated by Allied criticism of US targeting strategy. Concerns of Pentagon officials about NATO's limited utility were apparently taken on board in Washington without the United States even asking the Allies to give the Alliance a more substantial role.

On the European side, Allied officials complained that, after showing their support and willingness to contribute, the United States largely proceeded with a strategy focusing on dividing, not sharing, responsibilities. According to press reports, the situation irritated European leaders who, having given their strong political support, felt embarrassed about invoking Article 5 and then being left on the sidelines.

To some extent, the situation can be attributed to factors for which the Europeans themselves are to blame. First, they did not, for the most part, have significant military assets to contribute to the first phase of the Afghan campaign, which relied heavily on air-delivered, precision-guided munitions. Second, US officials were fully aware of past opposition of certain NATO members to involving the Alliance in military operations beyond their borders, to say nothing of beyond Europe.

On the other hand, the United States may have missed an opportunity to move the NATO consensus beyond the 1999 Strategic Concept following the 11 September attacks. Given invocation of Article 5 and the explicit willingness of many NATO Allies to contribute military capabilities to the war against terrorism, a political consensus existed that could have been used to expand NATO's horizons and establish a mechanism for NATO contributions in the future. This still could happen. But the politics of moving NATO more decisively into counter-terrorist operations have become even more difficult as time has passed and the horror, compassion and sense of community engendered by 11 September has faded.

If, however, the war against international terrorism remains for some years the main focus of US security policy, NATO's ability to be part of the solution could exert a major influence on US perceptions of the Alliance's utility. Dealing with this challenge — NATO's first true "crisis" of the 21st century — will require sophisticated political management on both sides of the Atlantic. The United States will have to be careful to ask Allies to do things that they are capable of doing. At the same time, the NATO Allies must avoid the perception that they do not support the United States in responding to the terrorist threat.

For NATO, not doing enough risks losing US interest in the Alliance. The disarray among members of the European Union, apparent at the European Council's December summit, and the failure of most EU members to commit additional resources to defence are interpreted in Washington as a lack of serious intent as well as effort. On the other hand, US attempts to push the Alliance beyond the political consensus concerning NATO's mission could create splits among the Allies and even domestic unrest in some Allied countries. In any case, the war against international terrorism will likely remain for many years the most important part of the political and strategic environment in which the NATO nations deal with every issue they face as Allies.