The Department of Defense derived from the National Security Act of 1947 which combined the War Department and the Navy Department. It was known originally as the National Military Establishment for a couple of years until the name was changed to the Department of Defense.
As long as we are going to be involved in on the world stage as an country operating in a militarily offensive mode the name Department of Defense is misleading and is not a true reflection of how we operate.
I hereby petition for the name to return to its origins and be referred to henceforth as the Department of War. There is no shame in being clearer about our role with regards to enemies both externally and internally to the United States of America.