The most accurate summary of the involvement of the United States in World War I is: "Initially, the U.S. was politically neutral and was involved only economically; however, once the U.S. entered the war its military involvement helped force an armistice."
This statement reflects the U.S.'s initial stance of neutrality, its economic support to the Allies, and the significant shift that occurred when the U.S. entered the war militarily in 1917, contributing to the eventual armistice.