Article 5 has been invoked only once – in response to the 9/11 terrorist attacks in the US in 2001. After the fall of the Berlin Wall and the collapse of the Soviet Union, a period of enlargement began which saw new democracies such as Hungary, Poland and Estonia join. The most recent members are Finland and Sweden, which applied to join in the aftermath of Russia’s invasion of Ukraine. After Donald Trump became president in 2016, Nato came under new pressure, with the president chastising fellow members for not spending enough on defence. This, coupled with the renewed threat from Russia, saw almost all members agree to raise defence spending in June 2025.

Source: The Guardian January 21, 2026 15:24 UTC