Posse Comitatus Act, 1878
Congress passed the Posse Comitatus Act to end military enforcement of Reconstruction in the former Confederacy. The law prohibited federal troops from executing domestic laws except when expressly authorized. It codified the American tradition that military interference in civilian affairs threatens democracy and liberty.
Federal troops withdrew from Southern states, effectively ending Reconstruction.
Created enduring legal framework limiting domestic military deployments, with exceptions like the Insurrection Act.
The Illinois case resurrects the core question behind Posse Comitatus: when, if ever, should military forces police American citizens? Judge Perry ruled Trump's deployment violated the Act's spirit and letter.
