The Union used military tribunals during and in the immediate aftermath of the American Civil War[2]. Military tribunals were used to try Native Americans who fought the United States during the Indian Wars which occurred during the Civil War; the thirty-eight people who were executed after the Dakota War of 1862 were sentenced by a military tribunal. The so-called Lincoln conspirators were also tried by military commission in the spring and summer of 1865. The most prominent civilians tried in this way were Democratic politicians Clement L. Vallandigham, Lambdin P. Milligan, and Benjamin Gwynn Harris. All were convicted, and Harris was expelled from the Congress as a result. It must be noted that all of these tribunals were concluded prior to the Supreme Court's decision in Milligan.
The use of military tribunals in cases of civilians was often controversial, as tribunals represented a form of justice alien to the common law, which governs criminal justice in the United States, and provides for trial by jury, the presumption of innocence, forbids secret evidence, and provides for public proceedings. Critics of the Civil War military tribunals charged that they had become a political weapon, for which the accused had no legal recourse to the regularly constituted courts, and no recourse whatsoever except through an appeal to the President. The U. S. Supreme Court agreed, and unanimously ruled that military tribunals used to try civilians in any jurisdiction where the civil courts were functioning were unconstitutional, with its decision in Ex Parte Milligan, 71 U.S. 2 (1866).