Question: What idea was used to justify u.s. foreign policy during the cold war era?
Disambiguated questions and answers: question: What ideas were used to justify u.s. foreign policy during the cold war era?
What doctrine was used to justify u.s. foreign policy during the cold war era?
answer: deterrence and containment
Truman Doctrine
Natural Questions answer: containment (from the Wikipedia article "Foreign policy of the United States")