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 command (COCOM), a specific type of nontransferable command authority over assigned forces, regardless of branch of service, that is vested only in the CCDRs by federal law in . The chain of command for operational purposes (per the Goldwater–Nichols Act) goes from the President through the Secretary of Defense to the combatant commanders. The current system of unified commands in the US military emerged during World War II with the establishment of geographic theaters of operation composed of forces from multiple service branches that reported to a single commander who was supported by a joint staff. A unified command structure