The Truman Doctrine
("The Truman Doctrine and Marshall").
"In 1947, two important events occurred: firstly, President Truman warned the American Congress that it was America's [responsibility] to contain Communism [in order to protect the sovereign rights of foreign nations]- this became known as the Truman Doctrine"
("Truman Doctrine (1947)").
The Marshall Plan
"General George Marshall came up with a plan to help Europe recover from the war using American money - this became known as the Marshall Plan."
("The Truman Doctrine and Marshall").
The Domino Theory
"The domino theory was a foreign policy theory during the 1950s to 1980s, promoted at times by the government of the United States, that speculated that if one land in a region came under the influence of communism, then the surrounding countries would follow in a domino effect. The domino effect suggests that some change, small in itself, will cause a similar change nearby, which then will cause another similar change, and so on in linear sequence, by analogy to a falling row of dominoes standing on end. The domino theory was used by successive United States administrations during the Cold War" [to assert the responsibility of America to intervene].
("Domino Theory").
The clip below shows Presidents Eisenhower and Nixon stating that it is the United States' responsibility to intervene in Vietnam to protect Vietnam's (and the nations around them) sovereign rights. However, President Nixon declares that the United States has a responsibility to intervene in order to safeguard its own security ("Domino Theory") (De'Gaule).
(De'Gaule).