What Day Was the founding of NATO?

About this date

Twelve countries, including the United States, Canada, the United Kingdom, and France, signed the North Atlantic Treaty in Washington, D.C., establishing NATO as a collective-defense military alliance.

The treaty's central Article 5 provision — that an armed attack against one member is treated as an attack against all — became the alliance's defining principle throughout the Cold War.

NATO has since expanded well beyond its original 12 founding members, particularly after the end of the Cold War, as a number of former Eastern Bloc countries joined in subsequent decades.

The Soviet Union responded to NATO's expansion in the mid-1950s by forming its own rival military alliance, the Warsaw Pact, formalizing the Cold War's bipolar military structure in Europe.

The alliance's founding treaty was signed against the backdrop of the Berlin Blockade, a major Cold War crisis the previous year that had underscored Western European countries' desire for a formal US security guarantee.