North Atlantic Treaty
The North Atlantic Treaty is the treaty that brought NATO into existence, signed in Washington, DC on April 4, 1949. The original twelve nations that signed it and thus became the founding members of NATO were the following:
The key section of the treaty was Article V which committed each member state to consider an armed attack against one state to be an armed attack against all states. The treaty was created with an armed attack by the Soviet Union against Western Europe in mind, but the mutual self-defense clause was never invoked during the Cold War. Rather, it was invoked for the first time in 2001 in response to the September 11, 2001 attacks against the World Trade Center and The Pentagon.