What was NATO?
Answer
The North Atlantic Treaty Organization
Explanation
NATO is the North Atlantic Treaty Organization, a military alliance founded on April 4, 1949 to provide collective defense against Soviet aggression and to anchor the United States in postwar European security. The North Atlantic Treaty was signed in Washington, D.C. by 12 founding members: the United States, the United Kingdom, Canada, France, Italy, Belgium, the Netherlands, Luxembourg, Norway, Denmark, Iceland, and Portugal. The Senate ratified the treaty on July 21, 1949 by a vote of 82 to 13, marking the first peacetime military alliance the United States had joined since 1778.
The core promise of NATO is contained in Article 5, which states that an armed attack on one member shall be considered an attack on them all, and that each ally will assist the attacked member with such action as it deems necessary, including the use of armed force. Article 5 has been invoked only once, on September 12, 2001, the day after the attacks on the United States. NATO's first Secretary General, British General Hastings Ismay, famously summarized the alliance's purpose as keeping the Russians out, the Americans in, and the Germans down.
The alliance grew steadily during the Cold War. Greece and Turkey joined in 1952, West Germany in 1955, and Spain in 1982. The Soviet Union responded to NATO by founding the Warsaw Pact in 1955.
After the Cold War ended, NATO expanded eastward in several rounds. The Czech Republic, Hungary, and Poland joined in 1999. Bulgaria, Estonia, Latvia, Lithuania, Romania, Slovakia, and Slovenia joined in 2004. Albania and Croatia joined in 2009, Montenegro in 2017, North Macedonia in 2020, Finland in 2023, and Sweden in 2024, bringing the alliance to 32 members.
NATO operations beyond mutual defense have included peacekeeping in Bosnia after 1995, the air war over Kosovo in 1999, the operation in Afghanistan from 2001 to 2021, and a counter-piracy mission off the coast of Somalia. The alliance's headquarters is in Brussels, Belgium. Supreme Allied Commander Europe, always an American officer, oversees military operations, while a North Atlantic Council of ambassadors handles political decisions. NATO remains the central pillar of the modern American alliance system.
Why this matters for your test
USCIS asks about NATO because it is the most important American military alliance and a defining feature of postwar United States foreign policy. Knowing NATO helps applicants understand why American troops are stationed in Europe and why events in places like Ukraine matter to the United States.
Source: USCIS 128 Civics Questions (2025)
