Short answers, pulled from the story.
NATO, the North Atlantic Treaty Organization, is an intergovernmental military alliance of 32 member states, 30 in Europe and two in North America. It serves as a system of collective security and deterrence, with members agreeing to defend each other from outside attack.
NATO was established with the signing of the North Atlantic Treaty on the 4th of April 1949. The 12 founding members were Belgium, Canada, Denmark, France, Iceland, Italy, Luxembourg, the Netherlands, Norway, Portugal, the United Kingdom, and the United States.
Article 5 states that an armed attack against one member shall be considered an attack against them all. It was invoked for the only time by the United States after the September 11 attacks, confirmed on the 4th of October 2001, leading to NATO involvement in Afghanistan.
Finland joined NATO in 2023 and Sweden joined in 2024. Both were spurred on to join by the Russo-Ukrainian war, and they are the alliance's newest members.
Each NATO member has committed to spending at least 5% of its gross domestic product on its own defense. The combined military spending of NATO members makes up over half of the world total, and in 2026 the shared budget was around €5 billion split between all 32 members.
Vladimir Putin has called NATO's eastward enlargement a threat since his 2007 Munich speech and opposes Ukraine joining the alliance. Russian leaders point to 1990 assurances given to Mikhail Gorbachev that NATO would not expand east.
NATO's main headquarters are in Brussels, Belgium, while its military headquarters are near Mons, Belgium. The North Atlantic Council, which holds effective governance authority, convenes at least once a week.