The North Atlantic Treaty Organization, or NATO was started on April 4th, 1949 after the North Atlantic Treaty was signed. The organization was started for three reasons: incouraging European integration, deterring Soviet expansionism, and preventing the revival of national militarism in Europe via a strong North Atlantic presence in the continent. Communists with the help of the Soviet Union were threatening elected governments throughout Europe. The US decided that isolationism was no longer a good idea, and provided aid through their US Marshall Plan. As the number of countries belonging to the organizaton grew, the Soviet Union felt they needed to form a kind of counter-organization. They called this the Warsaw Pact, and it was formed in 1955. During this time NATO formed the strategic doctorine of "Massive Retaliation." This stated that if the Soviet Union attacked, NATO would respond with nuclear weapons.
NATO is still a live organization today. In 2010 the organiztion decided to commit itself to providing help in all parts of a crisis--before, during, and after. In recent years it has played crucial parts in the crisis in Lybia, where it protected civilians from the attacks of its own government. NATO's operation helped to end the Lybian crisis and provided hope that reconciliation and reconstruction are still possible.

Missions of NATO throughout History
1950s - Purely a defensive organization.
1960s - Became a political instrument for detente.
1990s - A tool for the stabilization of Eastern Europ and Central Asia through the incorporation of new Partners and Allies.
Now - Extending peace through the strategic projection of security.