The First World War produced America's first mass political imprisonment of the modern era: over two thousand prosecutions under the Espionage and Sedition Acts for speeches, articles, and leaflets against the war — Eugene Debs sentenced to ten years for a single speech at Canton, Ohio, and running for president from Atlanta Penitentiary with nearly a million votes; Kate Richards O'Hare, Rose Pastor Stokes, and the Socialist and IWW press swept wholesale into the courts.

Alongside them stood some 500 absolutist conscientious objectors court-martialed into Leavenworth and Alcatraz, where they were shackled to cell bars and fed bread and water; the Hutterite Hofer brothers died from their treatment at Leavenworth in 1918. The COs' prison strikes and the amnesty campaign that finally freed Debs in 1921 built the organizations — the ACLU first among them — that every later antiwar generation would inherit.