What are the requirements for a country to join NATO?
Executive summary
NATO’s “open door” means any European country that accepts the Washington Treaty and can contribute to North Atlantic security may seek membership; aspirants typically undergo a Membership Action Plan (MAP) or accession talks to meet political, economic and military criteria, and admission requires unanimous approval by existing members [1] [2] [3]. NATO assesses democratic governance, civilian control of the military, defence interoperability and protection of classified information, and evaluates whether a candidate would strengthen Alliance security [2] [3] [4].
1. What “open door” actually requires: the legal baseline
NATO formally frames enlargement through Article 10 of the North Atlantic Treaty and the Alliance’s open‑door policy: any European state that is willing “to further the principles” of the Treaty and to contribute to the security of the North Atlantic area is eligible to seek membership [1]. That legal baseline does not specify a single checklist; it sets a political standard that aspirant states must meet in practice through NATO procedures described below [1] [3].
2. The membership pathway: MAP, accession talks, or a direct route
Most recent entrants followed a two‑step pattern: an invitation to a Membership Action Plan (MAP) that provides tailored advice and benchmarks, followed by accession talks and unanimous ratification by members. NATO’s MAP is a guidance and reform process; it is not mandatory and completion does not guarantee membership — some states may move directly into accession talks once they show readiness [2] [5]. Historically, nearly every entrant since 1999 used a MAP, but NATO and applicants retain flexibility [1] [2].
3. Political and democratic requirements: what NATO looks for
NATO requires prospective members to uphold democratic institutions and rule of law, make progress toward market‑oriented economies, and be “good neighbours” who respect sovereignty — core political preconditions repeatedly cited in NATO briefing material and secondary summaries [2] [6]. The Alliance treats those reforms as preconditions because a candidate’s internal governance affects collective security and interoperability [2].
4. Defence and security criteria: interoperability and civilian control
Candidates must prepare armed forces under firm civilian control and align military structures, doctrine and capabilities with NATO standards. Invitees are assessed on resources, defence planning, and their ability to protect NATO classified information — practical, technical criteria discussed during accession sessions and negotiated contributions to the Alliance budget [3] [2].
5. Political calculus: will the candidate strengthen the Alliance?
Beyond technical compliance, NATO evaluates whether admitting a state advances the Alliance’s security and stability in Europe; Washington and member capitals effectively judge strategic value and potential risks before extension of an invitation [4]. That political calculus means enlargement is not purely legalistic: geopolitical considerations and member states’ domestic politics shape outcomes [4] [3].
6. Unanimity and ratification: the final gate
Admission to NATO requires unanimous consent of all current Allies. After accession talks an invitation is issued and an accession protocol is opened; each existing member must ratify that protocol under its own constitutional procedures before the applicant deposits its instrument of accession and becomes a full member [3] [2]. This unanimity requirement gives every member leverage to press additional demands or delay ratification [2].
7. Limitations, exceptions and real‑world flexibility
NATO’s procedures have shown flexibility: MAPs are tailored and not always a strict prerequisite, and political urgency has accelerated processes in certain cases. Sources note MAP participation is common but not strictly required, and NATO exercises discretion on timing and sequencing of technical reviews and ratifications [2] [1] [5]. Available sources do not mention a fixed numerical scoring system or single checklist that guarantees accession.
8. Competing viewpoints and implicit agendas
Official NATO sources emphasize open doors and objective criteria [1] [3]. Parliamentary and media analyses stress the political nature of enlargement — allies weigh strategic benefit and risk, and individual capitals may stall bids for bilateral reasons [2] [4]. That divergence reflects an implicit agenda: NATO presents enlargement as rules‑based, while members retain political discretion that can be used to advance national interests [1] [4].
9. How long it takes and why timing varies
The process can take years because candidates must reform institutions, restructure defence forces, and negotiate security arrangements; each member’s ratification timetable varies as well. Historical practice shows rounds of enlargement occur over long periods and are shaped by shifting geopolitics, not just checklist completion [2] [3] [4].
10. Bottom line for prospective members
To join, a European country must accept the Washington Treaty’s principles, demonstrate democratic governance and civilian control of the military, build interoperable forces and security systems, pass accession talks or a MAP process, and secure unanimous ratification from Allies — but political judgment about whether a state “strengthens the Alliance” is decisive at every stage [1] [2] [4].