A ministry of defence or defense (see spelling differences), also known as a department of defence or defense, is an often-used name for the part of a government responsible for matters of defence, found in states where the government is divided into ministries or departments. Such a department usually includes all branches of the military, and is usually controlled by a Defence Minister, Minister of Defence, or Secretary of Defense.
Historically, such departments were referred to as a Ministry of War or Department of War, although such departments generally had authority only over the army of a country, with a separate department governing other military branches. Prior to World War II, most "Ministries of War" were Army ministries, while the Navy and the Air Force, if it existed as a separate branch, had their own departments. As late as 1953, for example, the Soviet Union had a "Ministry of War" alongside a "Ministry of the Navy".
The tendency to consolidate and rename these departments, and to coordinate until then mostly separate components of defence (air, land, navy) arose after World War II.