a. Dissidents
Dissidents are people who directly oppose an idea or group of people. In this case, dissidents are people going directly against the US participation in World War I.
With the passage of the Espionage and Sedition Acts in 1917, it became illegal to speak or act against the government's decision to fight in the war. The government arrested people who protested, handed out pamphlets, or spoke against the war effort. Unions and suffragists were often targeted during the war as being in violation of the Sedition Act and were jailed.