The answer is B. Without the United States, the League lacked the firepower to actually make a huge difference without the individual nations suffering huge consequences. In turn, the League didn't do anything, thus they were ineffective and nothing but a figurehead for democracy and international peace.
In the 1930's Japan went to war with China. The United States supported China and placed a trade embargo on Japan so they couldn't get any supplies from the United States, particularly oil that might fuel Japan's military conquests.<span />