The "War Department" was a key government agency in the United States responsible for military affairs. Established in 1789, it managed the nation's army and oversaw military operations, logistics, and personnel. The department played a crucial role in various conflicts, including the American Civil War and World War I. In 1947, the War Department was reorganized and renamed the Department of Defense to better coordinate military efforts and address the complexities of modern warfare. This change aimed to unify the branches of the military, including the Army, Navy, and Air Force, under a single leadership structure.