In 1863, Abraham Lincoln issued “General Orders No. 100: Instructions for the Government of the Armies of the United States in the Field” (aka the “Lieber Code,” named for its primary author Franz Lieber). The Lieber Code was one of the first modern codifications regulating the conduct of the U.S. Army during times of conflict and is still referenced today in the Department of Defense’s Laws of War manual. Prior to the Lieber Code, most armies conducted themselves based upon customs and precedents. Following the Lieber Code, leaders around the world have worked to ratify both national and international agreements that govern the rules of war, including one of the most widely-adhered-to international treaties in existence, the Geneva Conventions of 1949. Although the Lieber Code was distributed to every Union general in 1863, there is debate as to the extent of its influence on the conduct of these generals during the Civil War.
The Union general whose name has been most associated with the rules of war during this era was William Tecumseh Sherman, a commander who led troops in numerous battles throughout the war but is best known for his “March to the Sea” through Georgia in 1864. William Tecumseh Sherman employed a strategy known as “hard war” or “total war,” which he claimed was essential for a Union victory in the Civil War, but which Southerners viewed as barbaric and cruel.