The NATO (North Atlantic Treaty Organisation) was established on

April 4, 1949
September 1, 1966
December 12, 1990
January 20, 1950

The correct answer is A. April 4, 1949.

NATO (North Atlantic Treaty Organization) is an intergovernmental military alliance between 30 North American and European countries. The organization implements the North Atlantic Treaty that was signed on 4 April 1949. NATO constitutes a system of collective security, whereby its independent member states agree to mutual defense in response to an attack by any external party. NATO’s headquarters are located in Haren, Brussels, Belgium, while the headquarters of Allied Command Operations is near Mons, Belgium.

The Treaty of Brussels was signed on 17 March 1948 by Belgium, the Netherlands, Luxembourg, France, and the United Kingdom. The treaty was a mutual defense pact in response to the perceived threat of the Soviet Union. The treaty was later expanded to include the United States, Canada, Portugal, Italy, Norway, Denmark, Iceland, and Greece.

The North Atlantic Treaty was signed on 4 April 1949 by the 12 original members of NATO. The treaty states that an attack on one member state is considered an attack on all member states. The treaty also establishes a council of representatives from each member state to coordinate policy.

NATO has played a major role in the Cold War, the War in Afghanistan, and the Libyan Civil War. NATO is currently involved in a number of operations around the world, including the NATO-led International Security Assistance Force in Afghanistan.

The following are the four options in the question:

A. April 4, 1949
B. September 1, 1966
C. December 12, 1990
D. January 20, 1950

Option A is the correct answer. NATO was established on April 4, 1949.

Option B is incorrect. NATO was not established on September 1, 1966.

Option C is incorrect. NATO was not established on December 12, 1990.

Option D is incorrect. NATO was not established on January 20, 1950.