The best explanation of the political role of the U.S. during World War I is:
Although the U.S. joined the war late, it played an influential role in the peace process.
The United States entered the war in 1917 but became a significant player in the negotiations that led to the Treaty of Versailles and the end of the war, shaping the post-war order and establishing the League of Nations, despite not joining the League later on.