What major global event led to the United States adopting the policy of containment?

The adoption of the policy of containment by the United States was primarily driven by the geopolitical tensions and ideological conflict that emerged during the Cold War. Following World War II, the U.S. found itself in a position where the Soviet Union was expanding its influence across Eastern Europe and beyond, promoting communism as an alternative to capitalism and democracy.

Containment was formulated as a response to the perceived threat that communism posed to free societies worldwide. The policy aimed to stop the spread of Soviet influence rather than roll it back where it had already taken hold. This doctrine was articulated through various strategies, including economic aid through programs like the Marshall Plan, military alliances such as NATO, and involvement in conflicts like the Korean War, all aimed at containing the communist threat.

The other events listed, such as World War I and World War II, while significant in their own right, set the stage for global dynamics and power shifts but did not directly lead to the containment policy. The Great Depression impacted the U.S. economy and domestic policies but was not a catalyst for the Cold War strategy of containment. Thus, the Cold War is accurately identified as the major global event that prompted the U.S. to adopt this critical foreign policy strategy.