Everything You Need to Know About NATO

NATO has increasingly found itself in the spotlight since Russia invaded Ukraine in February 2022, with new countries seeking membership and former President Donald Trump, once again a candidate for the presidency, expressing a willingness to disregard the basic premise of the alliance.

NATO’s 12 founding countries formed the political and military alliance in 1949 in hopes of countering the post-war expansion of the Soviet Union. The organization has since grown to 31 members across North America and Europe, with Finland being its newest member, and it could soon expand to 32.

The accession of Sweden to the military alliance has been held up since July 2022, with Hungary being the lone country to have not given its approval.

The core of NATO’s founding document is Article 5, which outlines the principle of collective defense that still defines the alliance today: If one member country is attacked, it will be considered an attack on all member countries, who in response will each take “action as it deems necessary.”

Here’s everything you need to know about the history, membership and structure of NATO.

NATO was largely formed in response to the threat posed by the Soviet Union after World War II. Western Europe and the U.S. were wary of Soviet expansion as the USSR installed communist governments throughout Eastern Europe. By creating a military and political alliance, the founding members hoped to deter further expansion and ensure collective security for their allies.

Twelve founding countries signed the North Atlantic Treaty in April 1949, creating the alliance: Belgium, Canada, Denmark, France, Iceland, Italy, Luxembourg, the Netherlands, Norway, Portugal, the United Kingdom and the United States.

Finland is the most recent member of the alliance, joining in April 2023. It applied for membership in May 2022 alongside Sweden, and both countries became official invitees in July 2022. However, only Finland’s Accession Protocol has been ratified.

As stated in Article 10 of the North Atlantic Treaty, member countries may “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.” This article has been commonly referred to as NATO’s “open door policy.”

All NATO members must ratify an aspirant country’s accession for it to join the alliance. Because accessions must be unanimous, every member country effectively has veto power over additions to the alliance, as seen in Turkey and Hungary’s initial refusals to approve Sweden and Finland’s accessions.

Ukraine is not a member of NATO. At NATO’s summit in Bucharest in 2008, the allies declared that Ukraine and Georgia would become members of the alliance in the future, but Ukraine remains a NATO partner country today.

Since Russia’s invasion in 2022, Ukrainian President Volodymyr Zelenskyy has ardently campaigned for NATO membership for Ukraine.

NATO member countries have supported Ukraine throughout the war, and have sent tens of billions of dollars in economic, military and humanitarian aid to the country since Russia’s invasion in February 2022.

Though NATO is a political as well as a military alliance, collective defense is the heart of NATO’s founding treaty: All allies are committed to treating an attack on one member country as an attack on all member countries.

NATO coordinates military and defense measures among its member countries. On Sept. 12, 2001, the alliance invoked Article 5 for the first and only time in response to the terrorist attacks of 9/11 on the United States, which led to the invasion of Afghanistan by the U.S. and NATO allies.

NATO is headquartered in Brussels, Belgium, where each of its 31 member countries has a permanent delegation. Representatives from each member country convene through the North Atlantic Council – NATO’s main decision-making body – which is chaired by NATO’s Secretary General, currently Jens Stoltenberg of Norway. All allies must reach a consensus for a decision to be made, and each country gets one vote.

NATO is funded by its 31 member countries, and the United States, Germany and the United Kingdom are the largest contributors in total dollars. The alliance does not have its own army, and so its military operations are staffed by voluntary contributions from the member countries.

“Contributions vary in form and scale,” the organization’s website states. “For example, Allies can choose to contribute a few soldiers or thousands of troops to a NATO operation or mission. Contributions can also include any kind of materiel, from armoured vehicles, naval vessels or helicopters to all forms of equipment or support, medical or other.”

Member states have thus agreed to spend at least 2% of GDP on their own militaries. As of 2023, only 11 of the 31 NATO member countries meet that target, according to estimates published by the alliance. The three countries with the highest percentages are also the only ones that eclipse 3%: Poland (3.90%), the U.S. (3.49%) and Greece (3.01%). The other countries that meet the 2% threshold are Estonia, Finland, Hungary, Latvia, Lithuania, Romania, Slovakia and the U.K.

Elliott Davis Jr. contributed to this article.