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The North Atlantic Treaty Organization, NATO, is an intergovernmental military alliance governed by the North Atlantic Treaty or Washington Treaty, signed on April 4, 1949. The organization constitutes a collective defense system, in which the member states agree defend any of its members if they are attacked by an external power.
In 1954, the Soviet Union proposed its union with NATO, with the aim of maintaining peace in Europe, but the allies rejected the proposal. This, together with the incorporation of West Germany, (with the objective of preventing the expansion of communism) to the organization on May 9, 1955 - described as "a decisive moment in the history of our continent" by the Minister of Foreign Affairs of Norway, Halvard Lange- had as an immediate consequence the creation of the Warsaw Pact, signed on May 14, 1955 by the Soviet Union and its allies. This pact is considered the formal response to NATO, highlighting the two opposing sides of the Cold War.
