The best explanation for 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 U.S. entered the war in 1917, and although it fought for a relatively short time before the armistice in November 1918, it had a significant impact on the negotiations that followed, particularly through President Woodrow Wilson's Fourteen Points and the creation of the League of Nations.