President Truman had a serious tone to Congress in this address. The Truman Doctrine was a piece of foreign policy legislation that was a response to the rise of Soviet Russia and communism post World War II. Its aim was to prevent the spread of communism to free nations, or nations that were still suffering from the effects of the war. The U.S. saw the evils of communism and how it would take an already destroyed nation and plunge it into utter chaos. So they pledged political, economic, and even military assistance to nations who were susceptible to the rise of foreign or domestic authoritarian forces looking to use communism as their trojan horse to power. All of this was in an effort to contain communism to the nations it had already consumed (USSR, China, North Korea, etc.)