NATO Day Date in the current year: April 4, 2024

The North Atlantic Treaty Organization (NATO), also known as the North Atlantic Alliance, is an intergovernmental military alliance uniting 30 European and 2 North American states (as of March 2024). It is based on the principle of collective security: independent member states have a multilateral agreement to defend each other if attacked by third parties.

In the aftermath of World War II, France and the United Kingdom signed the Treaty of Alliance and Mutual Assistance, also known as the Treaty of Dunkirk, against possible attacks by Germany (and the Soviet Union, which was not stated in the treaty but heavily implied due the start of the Cold War). A little over a week later, U.S. President Harry S. Truman announced the Truman Doctrine that pledged American “support for democracies against authoritarian threats” (in other words, against the Soviet Union and other Communist regimes).

In 1948, the France-UK alliance was expanded by the Treaty of Brussels to include Belgium, Luxembourg, and the Netherlands. That same month, talks for a wider military alliance which could include North America in accordance with the Truman Doctrine started in United States. These talks eventually resulted in the formation of NATO.

The North Atlantic Treaty was signed on April 4, 1949 by the signatories of the Treaty of Brussels plus Canada, Denmark, Iceland, Italy, Norway, Portugal, and the United States. The treaty remained largely dormant for the next year or so, but the beginning of the Korean War showed that action needed to be taken. The Supreme Headquarters Allied Powers Europe (SHAPE) was founded in 1951, and the post of Secretary General of NATO was established in 1952.

NATO conducted no military operations during the Cold War, operating as a check on the threat posed by the Eastern Bloc. Its first operations were prompted by the Iraqi invasion of Kuwait in 1990. Since then, NATO has been involved in military operations in the Balkans, the Middle East, South Asia, and Africa.

Since it inception, NATO has added twenty new members. As of March 2024, the most recent member is Sweden, having jointed on March 7, 2024. Bosnia and Herzegovina, Georgia, and Ukraine are recognized by NATO as aspiring members (Ukraine formally applied to join the organization in September 2022, after being invaded by Russia).

NATO Day is celebrated in all member states of the North Atlantic Treaty Organization to commemorate its founding anniversary. It is marked by flag raising ceremonies and other events and activities. It should be noted, however, that not all member states celebrate NATO Day on April 4. In Romania, for example, it is observed on the first Sunday of April, and in Lithuania, it is celebrated on March 29 to commemorate the day when the country joined NATO.

NATO Day should not be confused with NATO Days in Ostrava. The latter is an annual security show held in the Czech Republic on the third weekend of September.