The best answer is D. They contributed to future conflicts by failing to resolve important issues.
The end of WWI and consequently the end of WWII were not enough to end the political and ideological disputes between the nations. Europe for the first time was not the strongest Imperialist empire it was in the past, and two different nations rise to power: The United States and the Soviet Union, with different ideological views about society. And because of this, we had different emerging conflicts such as the Korean War, the Vietnam war, and so many others.