World War I was underway in Europe for more than two years before the United States declared war on Germany in 1917. During that period of buildup to entering the war, the US government established mechanisms that would ensure citizens’ cooperation with the war effort. These efforts accelerated after war was declared. Because pacifism in general and opposition specifically to this war were widespread, there were significant government efforts to identify and weaken that opposition. These included the 1917 Espionage Act and the 1918 Sedition Act. The powers of the Department of Justice’s Bureau of Investigation, which later became the FBI, included enforcement of both acts.
One central target for this enforcement was the International Workers of the World (IWW), a socialist union, whose offices were frequently raided. Under the Sedition Act, one hundred IWW members were arrested and tried en masse in Chicago in 1918. A private organization, the American Protective League, was established with the authorization of the Justice Department; the APL specifically targeted Germans and German Americans.
In addition, conscription was instituted through the 1917 Selective Service Act. Draft registration was mandatory for eligible men, and failure to register was punishable by fines and imprisonment. Application of the provisions of these acts varied widely, with minorities and activists more likely to be jailed.