I believe the answer is B!
The United States failure to participate in the newly created League of Nations after World War I resulted in increased isolationism during the 1920's and early part of the 1930's. Many American citizens did not want to be involved in foreign affairs anymore. This is especially true considering the toll in both casualties and cost that World War I had on American citizens and the government. This resulted in the US playing a smaller role in international affairs and a refusal to join World War II until almost 2 years after it officially begins.
