A regional organization that was created in 1949 by nations including the United States, Canada, and most western European nations for mutual defense and has subsequently been expanded.?

North Atlantic Treaty Organization.

Explanation:

North Atlantic Treaty Organization (NATO) also famously know as North Atlantic alliance was formed in the period following world war second when the world was virtually divided between the two new superpowers the United States and Soviet Russia and their area of influence. The organization is formed in 1949 by the twelve nations aimed acted as a collective defense mechanism through which its member states commit to mutual defense in response to an attack by any outside party.