In Prague in January 1994, just after attending his first NATO summit in Brussels, US President Bill Clinton declared that it was no longer a question of whether NATO would enlarge, but how and when. Back then, however, huge differences still existed within the US government and in NATO about the wisdom of bringing former Soviet-bloc countries into the Alliance, and most Western officials (as well as those in Moscow) believed that the idea of NATO enlargement had been shelved in favour of the Partnership for Peace.

The uncertainty of the mid-1990s over whether enlargement would occur is a thing of the past. At the Alliance's Prague Summit in November this year, US President George W. Bush and his peers will issue invitations to the next group. And this event is likely to be preceded in May with the announcement of a new accord between NATO and Russia. What is uncertain, however, is who exactly NATO will deem ready to join. Even more uncertain is the role NATO will play in the world after taking the next steps on NATO-Russia and on enlargement.

Thanks to the jump-start given to enlargement by US Assistant Secretary of State Richard C. Holbrooke and his supporters in the US government in the autumn of 1994, NATO set out in 1995 on a slow and steady endeavour to bring in the first members. The timing was left deliberately vague until after Russian President Boris Yeltsin's re-election in July 1996, but with Yeltsin's second term secure, President Clinton recommended that the Alliance formally admit its newest members on the occasion of NATO's 50th anniversary celebration in the spring of 1999. There were some misgivings in the spring of 1997, especially in France, about the wisdom of proceeding if an accord could not be reached with Russia, but the NATO-Russia Founding Act was signed in Paris in May of that year. In July, invitations were then issued at NATO's Madrid Summit to the Czech Republic, Hungary and Poland. The only flare-up in the enlargement end-game occurred over the US decision to leave Romania and Slovenia out of the first round. This left France in particular unhappy, since Paris had already built support from a majority of the Allies to include the larger group.

In the United States, which was the main driver of the enlargement process between 1994 and 1997, the policy was made possible because a diverse group supported enlargement, albeit for very different reasons. The "Wilsonians", such as President Clinton and National Security Adviser Anthony Lake hoped that NATO enlargement would help encourage the adoption of market democracy and respect for human rights in Central and Eastern Europe, while the "hedgers", including then Senate Foreign Relations Chair Jesse Helms and prominent former officials Henry Kissinger and Zbigniew Brzezinski, emphasised expanding the Alliance to protect against the possible resurgence of Russia in the region.

In the first round of enlargement, the US Senate was particularly concerned by three main issues when it debated giving its consent to the accession of the Czech Republic, Hungary and Poland to NATO: the financial costs to current members, the reaction of Russia and the unwieldiness of a larger Alliance. Since it was difficult for senators to understand the NATO budget process, the potential costs were ambiguous, but the three candidates were believed sufficiently advanced economically to pay their way. The concern about Russia was tempered by Yeltsin's willingness to sign the Founding Act. And as far as the cohesion of a larger Alliance was concerned, NATO at 19 did not seem markedly different to NATO at 16.

The prospective second round of NATO's post-Cold War enlargement is not nearly as uncertain as the first. Many questioned the credibility of the "open-door" promise when no invitations were issued at NATO's 1999 50th anniversary summit in Washington. However, the creation at that time of the Membership Action Plan and, more importantly, the announcement that NATO would review the progress of the nine formal aspirants for membership at its 2002 summit did have the effect sought by enlargement proponents: it locked NATO into a process by which turning new members away in 2002 would cast severe doubts on the Alliance's credibility. When NATO Secretary General Lord Robertson said publicly in the summer of 2001 that the "zero option" was now "off the table" for the 2002 Prague Summit, NATO's next round of enlargement was no longer a question of when, but whom.

The second round is made easier by changes in the nature of the Europe-Russia-US relationship. In the early Clinton years, there were fears that Russia might abandon its efforts to reduce dramatically its nuclear arsenal or that a domestic backlash would lead to the return of Communists to power in the 1996 elections. In the first half of 2001, the Bush administration was less concerned about Russia's reaction than the Clinton team had been in 1996, because the new US foreign policy team did not see Russia as central to American diplomacy. There was also consensus that the main point of discord in Russian-US relations in the late 1990s had not been enlargement, which Russia could probably have accommodated in the spring of 1999 if that is all that NATO had done, but the Kosovo campaign. It was the latter that had caused Russian-US relations to deteriorate to their lowest level since the mid-1980s. Critically, in the wake of 11 September 2001, Russian-US relations have improved dramatically as President Vladimir Putin expressed an eagerness to cooperate in the campaign against terrorism and proposals for an enhanced NATO-Russian institutional relationship began circulating. As a result, the worries about Russia's reaction, that had been so great between 1994 and 1997, largely evaporated.

This is also the case for the Baltic Republics. President Yeltsin tried unsuccessfully to get President Clinton to shake hands in Helsinki in March 1997 on a "gentleman's agreement" that the Baltic nations of Estonia, Latvia and Lithuania would never become NATO members. Since then, Russia has had to accept that it is unable to prevent these countries from joining the Alliance.

That said, as NATO-Russia relations have improved, the issue of joint decision-making has come to the fore. Indeed, at the end of 2001, NATO and Russia announced that they would present details of a successor to the Permanent Joint Council (PJC), the NATO-Russia forum created by the 1997 Founding Act, by the May 2002 meeting of NATO foreign ministers. While optimism for the prospects of NATO-Russia relations has probably never been greater, the core problem that existed in the PJC will be difficult to overcome in a new body, given that NATO does distinguish between members and non-members. In the PJC, NATO had to reach a consensus at 19 before an issue was discussed with Russia. This structural feature meant that for the Allies, Russia's role largely appeared to be that of undermining agreement of the North Atlantic Council, while for Moscow, it seemed as if Russia was invited to the PJC simply to give NATO a green light to do whatever its members had already decided.

It is possible that NATO and Russia will develop a mechanism to give Russia a role in the decision-making process on some issues, such as combating terrorism and curbing the proliferation of weapons of mass destruction. However, the experience of the PJC and the Russian-US Joint Early Warning Center, both of which were unveiled amid great fanfare and then failed to live up to their billing, should leave us somewhat sober about what will actually be accomplished. New Russian personnel at NATO with both instructions and the ability to engage constructively with their counterparts will be important for ensuring that the new NATO-Russia body is more effective than its predecessor.

What is most remarkable about the second round of enlargement is not the absence of worry about Russia's reaction, but rather the lack of any debate so far about what enlargement will mean for the functioning of the Alliance. Perhaps going from 16 to 19 did not seem a major step. But what about going from 19 to 24 or even 26? If 2002 brings both an enhanced relationship with Russia as well as a big increase in members, then the future role of the Alliance may be profoundly affected.

Tough questions about what further enlargement means for the way in which NATO functions as an alliance are, however, likely to be raised when the US Senate debates the second round of enlargement. To some US legislators, this next round may not appear to add sufficiently to NATO's military capacity. This is in contrast to the first round, which - because it included a country of the size and resources of Poland - was believed to be adding to NATO's military capabilities. Since then, however, doubts have been raised about the ability of the first three new Allies to sustain their commitments. Moreover, the argument that long-standing Allies have as hard a time reaching spending targets does not play well with sceptics.

The question of the potential contributions of new members is even more glaring this time. In my view, a likely scenario for the Prague Summit is for invitations to be issued to the following five countries: Estonia, Latvia, Lithuania, Slovenia and Slovakia. Not inviting the Baltic Republics would be so obvious a sop to Russian chauvinism that it would be politically unacceptable. Slovenia has met the membership criteria since 1999, if not 1997. And Slovakia would have been included in the first round had it had a different government in the mid-1990s.

The problem, however, is that despite the willingness of all these aspirants and especially those in the Baltics to support the Alliance in general and the United States in particular, these countries have limited resources, populations and capabilities. Moreover, if elections in Slovakia next September produce a victory for the party of former Prime Minister Vladimir Meciar, that would leave four very small countries as the likeliest candidates. At least one country either of some size or geostrategic location is needed to make this round of enlargement look like a meaningful endeavour from a military point of view. This could open the door to Bulgaria and Romania. However, although both Sofia and Bucharest provided NATO with useful support during the Kosovo campaign, the political and economic difficulties that have plagued both countries over the years may prevent them taking advantage of the situation. While it may be true that enlargement has virtually nothing to do with enhancing capabilities, making it so flagrantly obvious could prompt a sharp debate about the purpose of the Alliance in the US Senate and elsewhere.

NATO has decided to explore the potential of creating a new NATO-Russia body and to take in at least some new members in 2002. What it has not done is engage in any real soul-searching about what role members expect NATO to play in the coming years as an alliance in responding to existing and future threats. While we often recall how critical NATO was for the Balkans in the 1990s, we tend to forget how critical the Balkans were for NATO. The missions in Bosnia and Herzegovina and Kosovo gave NATO a raison d'être after the collapse of the Soviet Union. But after 11 September, these missions will not be enough to keep NATO relevant during the coming decade. New threats to Europe and North America (as well as to Russia) emanate from outside Europe, not from the continent itself. NATO has yet to make the transition to an organisation that can protect its members against today's Article 5 threats. That is the fundamental challenge for NATO as it enlarges again and tries to work more closely with Russia.