Arising in the throes of the Civil War, Milligan limited the ability of the president to set aside the Constitution even in times of emergency -- specifically as regards President Lincoln's lifting of the right of habeas corpus.

The decision also rejected the federal government's attempt to use a military tribunal to try "a citizen who was neither a resident of a rebellious State nor a prisoner of war, nor a person in the military or naval service" for supporting the Confederacy during the ongoing war. The defendant in question was a citizen of Indiana.

Stay tuned for a more complete synopsis of this case. Also see Ex Parte McCardle (1869) for a similar issue.