Which peacekeeping organization was created after World War I, which the United States never joined and failed to prevent World War II?

• A. League of Nations
• B. United Nations
• C. NATO
• D. Warsaw Pact

Answer: (A)

The main idea here is recognizing the League of Nations as the international body created after World War I to keep the peace through collective security and dispute resolution. It was established in the aftermath of the war, largely championed by Woodrow Wilson, but the United States never joined because the Senate refused to ratify the treaty and commit to its obligations. Without U.S. participation, the League lacked the power and credibility to deter aggression. As the 1930s saw Japan, Italy, and Germany violate terms and pursue expansion, the League was unable to prevent another global conflict. By contrast, the United Nations formed after World War II with broader participation and stronger mechanisms for enforcement; NATO and the Warsaw Pact arose later during the Cold War, not in the post–World War I period, so they don’t fit the description of the question.