The United States Department of Defense is the federal agency responsible for providing the military forces necessary to deter war and ensure the security of the nation. It oversees all branches of the U.S. Armed Forces, including the Army, Navy, Air Force, Marine Corps, Space Force, Coast Guard, and National Guard, and coordinates a wide range of defense, humanitarian, and disaster relief missions both domestically and internationally. As one of the largest employers in the world, the Department of Defense offers diverse career opportunities for civilians and military personnel, supporting national security through innovation, training, and global operations.