In thinking through this answer, you will want to consider the following:
World War I marked the United States entrance on the global stage as a superpower in that the United States entered the war late with enough power to be taken seriously.
World War I marked an end of the "old" way of war and introduced new and vicious ways of fighting. Think about mustard gas and planes.
World War I's shaky conclusions set the stage for World War II. The Versailles Treaty bankrupted and demoralized the German people, setting the stage for the rise of the National Socialism party and scapegoating for German losses.
