Answer: 1.While avoiding the conflict until 1941, World War II marked a turning point for American isolationism. As Germany and Italy swept through Europe and North Africa, and Japan began taking over Eastern Asia, many Americans started to fear that the Axis powers might invade the Western Hemisphere next. By the end of 1940, American public opinion had started to shift in favor of using U.S. military forces to help defeat the Axis.
2.The benefits of Truman's offer to support any country trying to resist communism is the providing of economic aid to stabilize the economy which was affected by world war 11. In the case of Europe, 13 billion dollar was provided to stabilize the European economy.
Another benefits of Truman's offer was that it also help to improve the American economy, The aid (Marshall plan funds)given to the European was use to purchase American goods which leads to boost in the American economy.
3.The strategy of "containment" is best known as a Cold War foreign policy of the United States and its allies to prevent the spread of communism after the end of World War II.