2024年3月11日 · NATO was created by 12 countries from Europe and North America on 4 April 1949. Since then, 20 more countries have joined NATO through 10 rounds of enlargement (in 1952, 1955, 1982, 1999, 2004, 2009, 2017, 2020, 2023 and 2024). Article 10 of the North Atlantic Treaty sets out how countries can join the Alliance.