Define the truman doctrine how was it implemented in berlin?

Truman implemented this in response to two threats one being a communist-led uprising against the government in Greece and two being Soviet demands for some control of Turkey's Dardanelles. It was implemented in Berlin when Truman ordered U.S. planes to fly supplies to the people of West Berlin in response to the Soviet Union's 11 month blockade on Berlin.. or something among those lines

answer; it citizens provide a defense against foreign invaders;