The correct answer is: D) effectiveness
The League of Nations was created after WWI, it was established on January 10, 1920 by the Allied Powers. It's main purpose was to prevent the renewal of death and suffering caused by a war like the one that had just finished.
The United Nations was established on October 24, 1945 after WWII. It's main goal was similar to the one of the League of Nations, to "save succeding generations from the scourge of war...". In other words, to maintain peace and security as well as friendly relations betwwen nations.
As you can see, the League of Nations didn't succeed on preventing WWII, leading to millions of deaths. That is the reason it was considered a failure. The U.N. has at some point prevented great scale conlficts. One reason is that it has more members including the United States, which is a powerful ally.
