NATO open door policy
In the context of the enlargement of NATO, Article 10 of the North Atlantic Treaty is the origin for the April 1999 statement of a "NATO open door policy". History

Following the Eastern European Revolutions of 1989, countries from the former Eastern bloc became interested in joining NATO. During a March 1992 visit to Warsaw, NATO Secretary General Manfred Wörner said that the "doors to NATO are open". During the December 1994 OSSE conference in Budapest, the United States and its NATO allies stated that no European countries should be prevented from joining the alliance. On March 12, 1999, Poland, Hungary and the Czech Republic joined NATO as the first former Eastern Bloc states, beginning the expansion of NATO eastwards. When Estonia, Latvia, Lithuania, Bulgaria, Romania, Slovakia and Slovenia joined on March 29, 2004, U.S. President George W. Bush prepared for even further expansion of the alliance. During the welcoming ceremony held the same day, he said:

The April 2008 Bucharest Summit communiqué re-affirmed the NATO allies' "commitment to keeping NATO's door open to any European democracy willing and able to assume the responsibilities and obligations of membership, in accordance with Article 10 of the Washington Treaty." At that summit, Ukraine was invited to join the Alliance. In a December 5, 2015 "Statement by NATO Foreign Ministers on Open Door Policy" Montenegro was invited to join the alliance, and the signatories encouraged "Georgia to continue making full use of all the opportunities for coming closer to the Alliance." They remained "committed to the Open Door Policy, a founding principle of the Washington Treaty" and encouraged "partners to continue to implement the necessary reforms and decisions to prepare for membership," while they would "continue to offer political and practical support to the efforts" of the partners. At the end of November 2020, it became known that the NATO Summit in 2021 would consider a return to the open door policy, including the issue of providing Georgia with a Membership Action Plan (MAP). On February 9, 2021, the Prime Minister of Ukraine, Denys Shmyhal, stated that he hoped that Ukraine would be able to receive an action plan for NATO membership at the same time as Georgia. In response, the NATO Secretary-General confirmed during Shmyhal's visit to Brussels that Ukraine is a candidate for NATO membership. On June 14, 2021, a communiqué issued at 2021 Brussels summit reaffirmed commitment to the Open Door Policy, as well as "all elements" of the decision made at the 2008 Bucharest Summit that Georgia and Ukraine will become members of NATO. On January 7, 2022, ahead of a bilateral meeting with Russia, NATO Secretary-General Jens Stoltenberg said that "Russia's unprovoked and unjustified military buildup in and around Ukraine” had serious implications for European security and stability and that Russian forces were only strengthening a noose around Ukraine. A Ukrainian official said at the time that “There should not be any compromise with Russia... They recognize only force. Weakness will provoke them... NATO must show that doors are open and promises kept.” Stoltenberg said that “The Russian military buildup has not stopped. It continues and [is] gradually building up with more forces, more capabilities,” whereupon he described armored units, artillery, combat-ready troops, electronic warfare equipment, and other military capabilities. Stoltenberg was clear that the alliance would not heed Russia's demand to withdraw the invitation for Ukraine and Georgia to join NATO—or for any country to pursue the path of its choosing. On January 28, 2022, an op-ed was published by the New York University School of Law in which the author disclosed that in two drafts of a 2021 NATO-Russia treaty, "Moscow placed the onus of averting an expanded conflict in Ukraine on the West broadly, NATO particularly, and the United States specifically. Among other stipulations, Moscow insisted that NATO's open door to new members be shut." In the wake of the Russian invasion of Ukraine on February 24, 2022, 30 NATO Heads of State held a meeting on March 24, 2022 in Brussels and one result was a statement which read in part:

In May 2022, Turkey announced that while fully supporting NATO's open door policy, it opposed the memberships of Finland and Sweden for allegedly supporting terrorism. On March 17, 2023, Turkey withdrew its opposition to Finnish accession to NATO, enabling Finland to become the 31st NATO member state on April 4, 2023. On July 10, 2023, Turkey dropped its objection to Swedish accession to NATO, clearing the path for Sweden to become the 32nd NATO member state. References

Enlargement of intergovernmental organizations
Events affected by the Russian invasion of Ukraine
NATO