The Addition of NATO Members Over Time (1949-2024)

Author: Notre Dame International Security Center

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Updated March 8, 2024


When World War II ended in 1945, Europe lay in ruins. In the European theatre of the War alone, an estimated 15 million to 20 million people (combatants and non-combatants) lost their lives. It is the most destructive war in human history, and it changed the landscape of international relations forever. The former Nazi Germany was split into two: the democratic and capitalist West Germany and the communist and authoritarian East Germany. The United States and the Soviet Union emerged as the two global superpowers and rivals on the international stage, and the Cold War began. 

To secure peace and stability in Europe, in 1949, twelve countries on both sides of the Atlantic formed the North Atlantic Treaty Organization (NATO) as a means of ensuring their collective security. Today, there are 31 NATO members (with more applying at the time of this writing). So, how did we get here? 


Meant to unite ideologically likeminded cultures—namely, those who espouse democracy and liberalism—the North Atlantic Treaty was ratified in 1949, with 12 signatories. Listed alphabetically, they were: 

  1. Belgium 

  1. Canada 

  1. Denmark 

  1. France 

  1. Iceland 

  1. Italy 

  1. Luxembourg 

  1. Netherlands 

  1. Norway 

  1. Portugal 

  1. The United Kingdom 

  1. The United States 

Each of the twelve members agreed to the 14 articles outlined in the treaty. Any country wishing to join the Alliance must meet the economic and military strength requirements. The decision to add a new member state must be unanimously approved by the existing members. 

NATO has now gone through nine rounds of enlargement: 


Seven years after its establishment, NATO expanded for the first time just south of the Black Sea: 

  1. Greece 

  1. Turkey 


  1. West Germany 

When German reunification occurred in 1990, the former East Germany was also welcomed into the Alliance. 


  1. Spain 

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A 2017 illustration of NATO membership. North Macedonia joined in 2020.


At this point, we must mention the Warsaw Pact—the Soviet Union’s response to and equivalent of NATO. In total, there were 8 members of the Warsaw Pact. When the Soviet Union dissolved in 1991, so did the Warsaw Pact, and the Cold War ended.  

Also noteworthy: Yugoslavia (in southeast Europe) collapsed in 1992—dissolving into 6 successor states; some of which would also be interested in joining NATO. Yugoslavia was not aligned with NATO nor the Warsaw Pact, hence acting as a “buffer” between the alliances. 


No longer obliged to the Warsaw Pact, former Soviet allies turned their eyes toward NATO. Three former Warsaw Pact members were admitted into NATO

  1. The Czech Republic (formerly Czechoslovakia) 

  1. Hungary 

  1. Poland 


2004 brought the largest increase in NATO members since the Alliance’s foundation. Perhaps even more notable, though, is republics formerly of the Soviet Union were now joining (Estonia, Latvia, Lithuania). 

  1. Bulgaria (formerly of the Warsaw Pact) 

  1. Estonia 

  1. Latvia 

  1. Lithuania 

  1. Romania (formerly of the Warsaw Pact) 

  1. Slovakia  

  1. Slovenia (successor to Yugoslavia) 


In 2009, NATO’s foothold in East Europe grew firmer: 

  1. Albania (formerly of the Warsaw Pact) 

  1. Croatia (successor to Yugoslavia) 

2017 and 2020 

These additions to NATO are both successor states to Yugoslavia: 

  1. Montenegro (in 2017) 

  1. North Macedonia (in 2020) 

2023 and 2024

The Russo-Ukrainian War, and the escalation of which beginning on February 24, 2022, brought NATO’s growth into the foreground of foreign policy debates at the time. Russia’s full-scale invasion also prompted Finland and Sweden to officially apply and were eventually accepted into the alliance. 

  1. Finland (in 2023)

  2. Sweden (in 2024)


Where has the addition of NATO members led us? 

With NATO recognizing Bosnia and Herzegovina (successor to Yugoslavia), Georgia, and Ukraine (both former Soviet Republics) as aspiring members, does Russia’s leadership feel a pressure of NATO coming right up to their western doorstep?  

Did NATO’s eastward expansion directly lead to President Putin’s decision to invade Ukraine? If Russia’s goal was, in fact, to ensure a buffer between NATO and Russia, does the Finnish addition to NATO defeat the goal? What role may Serbia—another Yugoslav successor state: one closely aligned with Russia—play in the future? Does NATO’s expansion serve U.S. national security interests? 

To investigate these questions study at NDISC. We provide a place for national security scholars to explore these pressing issues. If you’re interested in these topics and making a difference in the future of foreign policy, consider studying with us at the Notre Dame International Security Center.