Why did the USA move from the isolationism that characterized America during the first half of the twentieth century to the interventionist that dominated the second half of the century?
The second half of the 20th Century saw America transit from their traditional roots of international isolationism to a superpower interventionist. The values that the American forefathers had laid down as their vision for the future of the nation were abandoned, becoming increasingly more involved in foreign affairs. The World Wars played a substantial role in America's conversion and significantly changed American views both politically and economically. Both Woodrow Wilson and F.D Roosevelt were dragged into wars they did not want to be a part of. After the sinking of the Lucitania and the attack on Pearl Harbour, the presidents were obligated to become involved in conflicts they did not care for. With the massive increase in the economy over this time and the threat of communism post WWII from the USSR, America became increasingly involved in overseas issues and became the interventionist we know today.
America became increasingly paranoid of a communist revolution post WWII and went to many extremes to stop that happening. Communism was such a danger to America because it went completely against their thesis of life; freedom, liberty and justice. With the war ending in Europe on May 8, 1945, the Russians planned on declaring war on the Japanese 90 days later, August 8, 1945. Many American politicians and military personnel new that a Russian invasion was immanent and were keen to get the war finished promptly. A diary entry of the Secretary of the Navy James Forrestal on July 28, 1945 described Secretary of State James F. Byrnes as: "most anxious to get the Japanese affair over with before the Russians got in."(1)
The Americans were desperate for the Japanese to surrender to them, so that they would control post war Japan, not the Soviet's, as it could have influenced them to become a communist superpower also. This resulted in the first atomic bomb being dropped on Nagasaki on August 6, 1945, attempting to make the Japanese surrender before the Russians had declared war. This not only resulted in the ending of the war, but ultimately stopped communism reaching any further at that particular point in time.
The conclusion of the war saw the Soviet's engage in Allied efforts, but never planned on joining them in their capitalistic ways. After the failure of an Allied Conference in London, December 16, 1947, it became abundantly clear to the West' that the USSR had become an unashamed expansionist, military power. Despite Allied efforts to rebuild much of Europe to stem the Communist influence, the paranoia was still ever present. The fundamental aim of the British post war policy was: "to ensure American power was not withdrawn from Europe"(2)
Britain knew that they could not longer prolong their role as the major influence in Europe, a role they had...