NATO From Article 5 to Eastern Sentry: 77 Years of Collective Defense

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NATO began in 1949 when 12 nations signed the Washington Treaty, partly drafted with the help of Canadian diplomat Lester B. Pearson, after the Treaty of Dunkirk in 1947 and the Brussels Treaty in 1948. It was a paper promise until the Korean War in 1950 pushed members to create SHAPE in 1951, standardizing artillery shells, radio protocols and even aviation fuel. West Germany's entry in 1955 prompted the Warsaw Pact, and through the Berlin Wall and France's 1966 exit from the military command the deterrence held. After 1990 the CFE Treaty scrapped 52,000 heavy weapons and Hungary, Poland and the Czech Republic joined in 1999.

The alliance fired its first shots in 1994, when NATO jets downed four Bosnian Serb warplanes, bombed in Bosnia after Srebrenica and ran a 78-day campaign over Kosovo without a UN mandate. Article 5 was first invoked after the attacks of September 11, 2001, leading to command of ISAF in Afghanistan. Crimea in 2014 brought the 2 percent pledge in Wales, and the 2022 invasion of Ukraine brought Finland and Sweden in. By 2025 Germany based an armored brigade in Lithuania and members set a 5 percent target for 2035, while a 2026 rift over the Strait of Hormuz tested the unanimity the North Atlantic Council requires.

• Gorbachev later said the 1990 assurances concerned non-German NATO forces in former East Germany, not wider expansion.
• Operation Deliberate Force in 1995 helped lead to the Dayton Agreement, and the KFOR peacekeeping force remains in Kosovo.
• Out-of-area missions stretched from a Libyan no-fly zone in 2011 to anti-piracy patrols in the Gulf of Aden.
• Operation Eastern Sentry followed Russian drone incursions into Polish airspace in 2025.
• Total alliance spending passed $1.5 trillion in 2025, with European and Canadian members alone above $608 billion.