[204] The debate touched on matters from technical feasibility to strategic value to the morality of creating a massively destructive weapon.[205][206] On January 31, 1950, Truman made the decision to go forward on the grounds that if the Soviets could make an H-bomb, the United States must do so as well and stay ahead in the nuclear arms race.[207][208] The development achieved fruition with the first U.S. H-bomb test on October 31, 1952, which was officially announced by Truman on January 7, 1953.[209]

Korean War
Further information: Korean War
President Truman signing a proclamation declaring a national emergency and authorizing U.S. entry into the Korean War
On June 25, 1950, the North Korean army under Kim Il-sung invaded South Korea, starting the Korean War. In the early weeks of the war, the North Koreans easily pushed back their southern counterparts.[210] Truman called for a naval blockade of Korea, only to learn that due to budget cutbacks, the U.S. Navy could not enforce such a measure.[211]
Truman promptly urged the United Nations to intervene; it did, authorizing troops under the UN flag led by U.S. General Douglas MacArthur. 