Answer:
Truman Doctrine was developed after the end of the World War II.
Step-by-step explanation:
After the end of World War II, Britain could no longer retain its influence and power over Greece and Turkey to suppress the emerging communist supremacy in these two countries.This responsibility of rendering military and economic aid to Greece and Turkey had to be transferred to U.S.
U.S took this task as an opportunity to exert its influence over other nations by establishing a doctrine which had democratic appeals. At this, President Harry S. Truman established the Truman Doctrine which aimed at providing political, military and economic aid to countries that were being suppressed by external or internal totalitarian control.
During this point of time, the Soviet Union was already emerging as a powerful communist regime. It was demanding control over some parts of Turkey. The U.S , therefore, had to intermediate and stop the Soviet forces from taking control over the Turkish government.
The U.S officially vowed to assist such countries who were under the threat of such control and, thus, established the Truman Doctrine. The Truman Doctrine was a declaration to Cold War between U.S and Soviet Union.