Which group was created during the Cold War to unify all of the member countries against communist aggression and formed a security alliance to defend each other? *

North Atlantic Treaty Organization, is the right answer.

Explanation:

Created in the year 1949 by the U.S., Canada and some other Western European Nations, NATO was an organization to provide collective security against communism or the Soviet Union.Following the end of World War II, the European Nations made efforts to restore their economics and ensure their security. NATO is a system of collective defense, in which all the member states agree to provide a mutual defense if any of member nation is attacked by any external nation.

Aor b but i'm going with b