Cause Effect The United States and the Soviet Union emerged as the world's two superpowers locked in a contest for supremacy. Which of the following best completes the chart? O A. The Soviet Union's population was at an all-time low after the war. B. The United States had gone through a sudden technological revolution. O C. The Yalta and Potsdam conferences neutralized many other world powers. e D. Other nations were devastated on a military and economic level after the war.