As expected, The Hague NATO summit held on 24-25 on June did not reaffirm the pledge it first made to Ukraine and Georgia in 2008, and repeated at every summit until now, that they would eventually join the alliance. The Trump administration is emphatically opposed, and NATO operates by consensus. The most the allies were prepared to do for Ukraine was to include their direct contributions to its defence and defence industries in the five per cent of GDP they committed to spend on defence and defence-related matters by 2035.

With Ukraine’s membership off the table, and unsure of Trump’s commitment to NATO, the allies also omitted any mention in the summit declaration that NATO remained open to new members.  That marked a break with language that had appeared in every summit declaration since 1994. Neither, however, did NATO leaders abandon the open-door policy. That, too, would have required consensus, and there are still many European leaders who ardently support expansion, even into the former Soviet Union, in large part to contain what they see as Russia’s ingrained imperialist ambitions.

Eventually, however, NATO will have to make explicit its position on new members. Ukrainian President Volodymyr Zelenskyy, who attended the summit, continues to make the case for membership, even if he acknowledges it will be unobtainable as long as war rages with Russia. More importantly, Russian President Vladimir Putin insists that there will be no end to the Russia-Ukraine war or the broader confrontation with the West unless NATO ends its open-door policy in writing. Sooner rather than later, NATO leaders will have to address the issue of expansion directly, as they position the alliance to deal with Russia in the years ahead.

Abandoning the policy will not prove easy, and many European leaders will be vehemently opposed. The open door has been entrenched in NATO rhetoric since the middle of the 1990s, but the current geopolitical situation in Europe and its probable evolution raise serous doubts about the wisdom of further expansion, at least eastwards into the former Soviet Union. Indeed, the history of NATO expansion, the evolution of the alliance’s mission, and the state of Russian power suggest it is time to close the door.

NATO boosters will argue that the alliance was created in 1949 with the door left open. Article 10 of the North Atlantic Treaty, its foundational document, states explicitly that the alliance ‘may, by unanimous agreement, invite any other European State in a position to further the principles of this Treaty and to contribute to the security of the North Atlantic area to accede to this Treaty’. In its initial years, NATO expanded to include Greece and Turkey (1952) and West Germany (1955). Spain joined in 1982, and Germany was reunified inside NATO in 1990.

NATO leaders did not, however, speak of an open door during the Cold War, as their successors have since its end. Cold War leaders were not interested in expansion so much as enhancing the alliance’s capacity to deter and contain Soviet expansionist impulses in Europe. The decisions to bring in new members were grounded in sober geopolitical calculations. NATO admitted Greece, Turkey, and eventually Spain to fortify its position in the Mediterranean and complicate the Soviets’ access to the oil-rich Middle East. NATO’s decisions on Germany bolstered the alliance’s capabilities on the central front, while creating conditions for German rearmament that did not unduly alarm those countries who had been victims of Nazi Germany’s savagery within living memory.

Talk of an open door would have been needlessly provocative, if not delusional. The continent was split between Western and Soviet camps, and those that belonged to neither – especially Sweden, Switzerland, and Yugoslavia – were profoundly jealous of their neutrality. The United States respected Soviet power and its sphere of influence. For that reason, it offered little material support to rebellious Soviet satellites during the Cold War. To have acted otherwise, it was believed, would have risked a third world war.

The geopolitics of expansion shifted radically with the end of the Cold War. The breakup of the Soviet Bloc and the Soviet Union, presented the United States with an historic opportunity to reshape the European continent to its enduring strategic benefit. It could hope to eliminate, for an historical era, the threat of a hostile power dominating Europe and thereby putting the United States’ own security at risk.

Russia, the chief successor to the Soviet Union, was weak and weakening. Its grip on Central East Europe was receding as its troops withdrew. It was in the midst of an accelerating systemic crisis that would turn the once fearsome Red Army into a motley crew of impoverished troops. In stark contrast to Cold War realities, Russian weakness raised greater alarm than Russian strength. Would rogue actors gain access to its massive arsenal of weapons of mass destruction? Would instability in Russia spill over into its newly sovereign and fragile neighbours?

Meanwhile, those neighbours proclaimed an interest in transitioning to free-market democracy. They wanted to join the West to gain the money and assistance they needed to stay afloat, recover, and reform. Integration, they thought, would bolster their security against any lingering or renewed Russian threat. Russian leaders likewise proclaimed their interest in free-market, democratic reform. They, too, sought close relations with the West and the United States in particular, but for the opposite reason: to maintain some residual power and influence over developments in the former Soviet Bloc and elsewhere in Europe.

To be sure, there were perils: the general instability in the East, the history of troubled relations among states in a region that had birthed two bloody world wars in the 20th century, and the spreading ethnic conflict in the Balkans and the Caucasus. But overall, the promise outweighed the risk by a wide margin.

In this fluid situation, the United States could aspire to achieve the goal first articulated by US President George H.W. Bush at the end of the Cold War: a Europe whole, free, and at peace. To that end, Washington endeavoured to stabilise Central East Europe and the former Soviet Union and integrate the newly sovereign states into Western-dominated structures grounded in democratic values. It sought to do that without alienating Russia: Washington needed to further the cooperative relations with Russia that had developed during the last years of the Cold War to ensure, at a minimum, reliable control over its nuclear arsenal. More importantly, Europe could never be at peace, if Russia was actively opposed.

The task was enormous. It called for subtlety, flexibility, and creativity. But Washington was not beginning with a blank slate. There was never any doubt that NATO would lie at the centre of US policy. The alliance anchored the United States in Europe; it was the foundation of its power. Calls from various quarters, especially Russia, to disband NATO now that it had accomplished its core mission of containing the Soviet threat fell on deaf ears in Washington. For the United States, there was one question: how to reimagine NATO for the current and evolving European security environment so as to perpetuate the United States’ pre-eminence on the continent.

The Clinton administration’s initial response was to launch the Partnership for Peace, in deference to Russia’s vehement opposition to NATO expansion. The programme was designed to allow all the newly sovereign states to affiliate with NATO and acquire the habits of security cooperation necessary for future membership.  Open to all, the programme would not draw a new dividing line in Europe, and thus could hardly be described as directed against Moscow (which eventually joined). To be sure, the Central East European states were disappointed – many had been pressing for NATO membership, including Ukraine and the Baltic states – but bowed to Washington’s preferences. Moscow, by contrast, was delighted. When informed of the programme, Russian President Boris Yeltsin exclaimed: ‘This is a brilliant idea, a stroke of genius.’

The administration’s enthusiasm for the Partnership was short-lived, however. Despite the rhetoric of partnership, it was increasingly troubled by Russia’s trajectory. Disturbing developments were accumulating:  Russia’s brutal, but ultimately lost war against Chechen separatists; the growing prominence of militant nationalists and unreconstructed communists in domestic politics; pervasive corruption and lawlessness. At the same time, pressure for expansion was mounting in the United States. Central East European diasporas (many located in electorally important states) were lobbying aggressively for it; vested interests in NATO inside the administration were pressing for a more ambitious role for the alliance; and anti-Russian forces in the political establishment were vigorously campaigning for continued containment of Russia.

All these circumstances inclined Clinton to rethink and accelerate his plans for expansion. Perhaps most important, in 1994 the geopolitical situation in Europe shifted in a way that favoured expansion. By the end of August, Moscow had withdrawn its final troops from Germany and the Baltic states. The risk of Russian mischief was greatly reduced. The United States could sharply discount Russian power.

By the summer of 1995, Clinton had decided to move forward with NATO expansion. Deputy Secretary of State Strobe Talbott made the public case. Expansion, he argued, would be evidence of continuing US engagement in Europe. It would nip emerging security conflicts, especially territorial disputes, in the bud by making their resolution a condition for membership. Similarly, it would encourage democratic transitions across Central East Europe by stipulating that only democracies could join what was now redefined as an alliance of democratic states.The end result, Talbott asserted, would be the enhancement of collective deterrence across the continent.

The deputy secretary did not hide the fact that expansion was a hedge against the return of an authoritarian, expansionist Russia. But he argued that the process would in fact be good for Russia: it would foster stability in a region that had produced two wars that had devastated the country. And he did not rule out Russian membership in the future. One day, he wrote, ‘a fully democratic Russia, at peace with its neighbours and with itself’ might join.

NATO’s door had been flung open. The 1997 Madrid summit invited the Czech Republic, Hungary, and Poland to begin accession talks, while affirming that NATO remained open to new members: ‘The Alliance will continue to welcome new members in a position to further the principles of the Treaty and contribute to security in the Euro-Atlantic area. The Alliance expects to extend further invitations in coming years to nations willing and able to assume the responsibilities and obligations of membership.’ NATO made good on its promise. Seven new states (Bulgaria, Estonia, Latvia, Lithuania, Romania, Slovakia and Slovenia) joined in 2004. Albania and Croatia entered in 2009, as did Montenegro in 2017 and North Macedonia in 2020. Finland and Sweden became members in 2023 and 2024, respectively.

Thus, for nearly three decades, the open-door policy has stood at the centere of NATO’s identity, exalted at official meetings and in documents. There is no evidence the alliance is prepared to revisit it, even if it was not mentioned in the most recent summit declaration. Indeed, there has been very little questioning of the policy since the US Congress and foreign policy establishment engaged in a sharp debate over its wisdom before the first wave of post-Cold War expansion in the late 1990s. Questions were then raised about its impact on the effectiveness of the alliance and the implications for relations with Russia. The debate was fierce. The country’s most renowned Russia expert, George Kennan, author of the policy of containment, stated bluntly that ‘expanding NATO would be the most fateful error of American policy in the entire post-cold-war era’.

In the end, the Senate voted 80-19 to approve the admission of the Czech Republic, Hungary, and Poland.  Then the debate magically vanished. Ninety or more senators approved each subsequent wave of expansion. Even the Trump administration, despite its deep doubts about NATO’s value, has yet to question the policy in general, although it has made clear its opposition to Ukraine’s membership. The open door has thus become, and remains, a core element of NATO’s identity and a key principle of US foreign and security policy.

US decisions on NATO expansion have always been inextricably tied to assessments of Russian power. No post-Cold War American administration has ever operated under the illusion that Russia might be anything other than emphatically opposed. Yeltsin repeatedly expressed, in the strongest terms, his opposition to Clinton. Putin has railed against NATO expansion for years. The issues for the United States have been what Russia could do in the real world to derail its initiatives and how far Washington had to go to assuage its concerns. Did Russia have the power to thwart the United States’ goals in Europe? How important was Russia to the advancement of US foreign-policy priorities?

Both the Clinton and George W. Bush administrations sought to mollify Russia, not only because that would ease the process of expansion, but also because they hoped for Russian cooperation on arms control and, particularly with regard to Bush, counterterrorism. Even though NATO remained at core a military alliance, both Clinton and Bush officials stressed the alliance’s growing political role, in advancing democracy, for example. In the hope of easing Russia’s perception of threat, Clinton drew down US forces in Europe from over 300,000 to just over 100,000, and both Clinton and Bush honoured the commitment made to Russia in the 1997 NATO-Russia Founding Act not to deploy nuclear weapons or station substantial combat forces in new members. Both created NATO-Russia fora to give Russia insight into but never, as they repeatedly stressed, a veto over NATO policies, including consideration of new members. They both maintained the fiction that membership remained open to Russia in the future, even though it was obvious to any attentive observer that Washington was never going to allow a country to join that had the resources and will to challenge its leadership of the alliance, as Russia did.

There were always limits to how far these two presidents would go in appeasing Russia, because in the end they both believed that Russia was too weak to offer any serious resistance to a process they considered critical to US security and global power. That view changed for subsequent administrations after Russia demonstrated in the short, victorious war against Georgia in 2008 that it was prepared to use force to defend its interests and prevent a country it considered vital to its own security from joining NATO. The reluctance with which NATO has moved on its promises of future membership to Georgia and Ukraine is stark evidence of how Russia’s exercise of power can shift NATO’s calculations. Expansion continued, to be sure, but only to states in the Western Balkans, which, for geographical reasons alone, were unlikely to be targets of overt Russian aggression.

The open-door policy emerged at a unique moment in European history, at a time of tremendous flux, when Russia was in the midst of a profound political and socio-economic crisis, in no position to defend its interests in Europe or to effectively resist NATO expansion towards its borders. That situation no longer obtains.  Russia is now prepared to use force to defend its interests, especially against states that aspire to NATO membership, witness Georgia and Ukraine. In this changed geopolitical environment, the United States needs to revive the serious debate about expansion it abandoned at the end of the 1990s as part of a larger discussion of NATO’s future. Does the open-door policy reflect today’s realities and NATO’s needs?

As a practical matter, expansion eastward into the former Soviet Union has come to an end. Since 2008, when NATO first said that Ukraine would become a member, the alliance has demonstrated that it is not prepared to go to war against Russia to defend it, as it is assumed it would for a member. In 2014, when Russia annexed Crimea and fomented rebellion in the Donbas, the United States and its NATO allies basically stayed on the sidelines, providing no real military assistance and levying only minor sanctions. The United States, for its part, still hoped to work with Russia to contain Iran’s nuclear ambitions and crush the Islamic State in Iraq and Syria. In 2022, when Russia launched its massive invasion, US and allied support for Ukraine was much more robust: substantial military and intelligence support and harsh and escalating sets of economic and diplomatic sanctions against Russia. But no ally was prepared to put boots on the ground to battle Russian forces, and the United States and others carefully calibrated the types of weapons they provided Ukraine to reduce the risk of escalating the conflict with Russia.

If the United States and its allies are not prepared to risk war with Russia to defend Ukraine, what are the odds that they are prepared to do that for Belarus (a Russian ally), Moldova (constitutionally committed to neutrality), or Armenia, Azerbaijan, or Georgia, three Caucasian states that Europeans doubt are fully European?

So why continue to insist that the door is open? In part, it is a matter of pride: NATO leaders are loath to walk back on the promise they made to Georgia and Ukraine in 2008. They fear that doing so would make them appear feckless. In part, it is a matter of nostalgia: NATO leaders want to believe that a Europe whole, free, and at peace remains possible. They are not prepared to abandon hope.

Regardless, commitment to the open-door policy makes Europe a more dangerous place. It prevents fashioning a policy toward Russia that will provide stability. The Kremlin is not wrong that NATO expansion has been directed against Russia. They are only wrong in the aims and motivations behind it. US and NATO leaders have no plans to attack Russia, they are not contemplating forceful regime change in Russia. Rather, Washington has pursued expansion to prevent the re-emergence of a threat of Soviet dimensions on the European continent, and the only country that could conceivably pose such a threat was Russia. Expansion has been geopolitically defensive, not offensive from Washington’s standpoint.

And it has largely achieved its goal. Nearly 30 years after the first Cold War wave, it is inconceivable that Russia could dominate Europe, even if, as its war against Ukraine demonstrates, it can still devastate regions along its borders. NATO expansion has pushed the line dividing Russia from the West to the furthest eastern position since the end of the 18th century. Russia has been marginalised as an actor in Europe.

The task for the West today is to defend and stabilise that line, which now stretches from the Barents Sea to the Black Sea, and help Ukraine ensure that the segment that runs through it lies as close to its 1991 eastern border as possible. NATO does not need to expand further to the East to defend itself against Russia. In time, as was true during the Cold War, it should prove possible to reach arms-control agreements with Russia to reduce tension along the West-Russia frontier. That will, however, require the United States and its allies to recognise the new dividing line and respect Russian power to the east of it. And that means it is time to close the door on NATO expansion rhetorically and doctrinally, as the alliance has already done in practice.