The Truman Doctrine was the event that triggered off the Cold War.
Explanation: Both parties were mutually hostile and did not believe in a possible peaceful coexistence anymore. The Americans and Soviets’ hostility to each other as well as the belief that they could no longer cooperate after the start of the Cold War resulted in the Berlin Blockade. Thus, I can conclude that the Truman Doctrine marked the start of the Cold War.
