Theory of everything differ both from gravity and from electromagnetism. A further hurdle was the acceptance that in a TOE, quantum mechanics had to be incorporated from the start, rather than emerging as a consequence of a deterministic unified theory, as Einstein had hoped. Gravity and electromagnetism could always peacefully coexist as entries in a list of classical forces, but for many years it seemed that gravity could not even be incorporated into the quantum framework, let alone unified with the other fundamental forces. For this reason, work on unification, for much of the twentieth century, focused on understanding the three "quantum" forces:
Unified combatant command forces in an efficient "unified combatant command" force. Furthermore, the Secretaries of the Military Departments (i.e. Secretary of the Army, Secretary of the Navy, and the Secretary of the Air Force) are legally responsible to "organize, train and equip" combatant forces and, as directed by the Secretary of Defense, assign their forces for use by the combatant commands. The Secretaries of the Military Departments also do not exercise any operational control over their forces. Each combatant command can be led by a generalor flag officer from any of the military services. Unified combatant command A unified combatant command (UCC) is