The correct answer is Propaganda.
The United States used propaganda to win public support for the war.
The Government of the United States created an independent agency that tried to convince the U.S. citizens that entering the war was a good option. In 1917, the American government created the Committee on Public Information or CPI. Also known as the Creel Committee, the agency had the purpose of convincing American citizens that the participation on WWI was a good decision. The CPI used propaganda to influence public opinion.