By the end of the 1940s, the US and its allies managed to contain Soviet expansion in Europe, blunting Soviet efforts in Greece and Turkey and using the billions of aid in the Marshall Plan to weaken the appeal of communism in Western Europe. Yet containment was bound to be challenged in regions or types of conflicts where the extent and scope of national interest was ambiguous. Policymakers fixated on potential moves by Moscow, especially against Berlin, and Truman administration officials publicly downplayed any intent of deploying forces to the mainland of Asia. They apparently devoted little thought to Korea. When forces from the north stormed into the south in June 1950, likely at Stalin’s behest, Truman stunned the Soviet Union with the decision to resist by force. Truman was even able to pass a Security Council resolution organizing a military coalition to resist the invasion, as the Soviet Union was boycotting the body over its refusal to grant China’s permanent seat to the Communist Party, which seized power in Beijing the previous October.

Communist aggression fit into an American narrative of good versus evil, but America could not wage a total war without the risk of direct, potentially nuclear, conflict with the USSR.