France and Britain suggested the idea of NATO to America. American senators and representatives wanted to go back to isolationism so they were hesitant. U.S. legislators were also worried the European countries would become too dependent on America's support for their defense. Some also thought that countries like England would use America’s resources to maintain control over their colonies instead of using the support for protection. Eventually, American legislators were persuaded. Negotiations started on December 10, 1948. They agreed collective defense should be the focus of the treaty. After the original twelve countries agreed to the Treaty it was signed on April 4, 1949 ​​​​​​​

"It was only the second military alliance that the US had concluded in its history (the first was with France and dates back to the 1780s). So NATO marked the US turning its back on isolationism and neutrality after 1945 and taking on a new global role as the guardian of the international liberal order-a role which is just as necessary today as it was back in 1949." - Jamie Shea, the retired Deputy Assistant Secretary-General for External Relations.

The treaty itself consists of fourteen articles. The most important article is five, which embodies mutual defense the most. Article five states: “The Parties agree that an armed attack against one or more of them in Europe or North America shall be considered an attack against them all and consequently they agree that, if such an armed attack occurs, each of them, in exercise of the right of individual or collective self-defense recognized by Article 51 of the Charter of the United Nations, will assist the Party or Parties so attacked by taking forthwith, individually and in concert with the other Parties, such action as it deems necessary, including the use of armed force, to restore and maintain the security of the North Atlantic area.” This is important because It describes what the treaty does to protect its members.