The correct answer is: "During the Cold War era the US adopted the policy of containment".
After WWII, The US had adopted the containment strategy, a foreign affairs approach which focused on stopping the spread of communism worldwide. This is why the US started the Marshall Plan initiative, and sent financial aid to help rebuild Western European countries, in order to set an alliance with them against the expansion of the URSS that had already turned many Eastern European countries into Soviet republics, soon after the end of WWII.
This postwar attitude sharply contrasts with the former isolationism, through which the US aimed to avoid economic or political entanglements abroad.
