Final answer:
NATO, or the North Atlantic Treaty Organization, is the cooperative defense alliance between the US, Canada, and various European nations, aimed at securing peace and preventing Soviet expansion during the Cold War.
Step-by-step explanation:
The organization that represents the shared security interests of the United States and other Western European nations is the North Atlantic Treaty Organization (NATO). Formed in the aftermath of World War II, NATO was principally designed as a collective defense mechanism against possible Soviet aggression, underscoring the commitment to mutual military assistance among member states. Its goal is not expansion but the preservation of peace and security in Europe. Originally comprised of Western European countries and the United States, NATO has since grown to include Eastern European countries such as Turkey.
During periods when the Soviet Union exercised its veto power within the United Nations Security Council, Western European nations recognized the need to establish an alternative means of protection, which led to the creation of NATO in April 1949. The organization enacted a policy where an armed attack against one member was considered an attack against all, creating a standing army ready to defend Western Europe. Over time, NATO evolved to address broader security issues and foster stability within the transatlantic region.