Classical unified field theories a survey of classical relativistic field theories of gravitation that have been motivated by theoretical concerns other than unification, see Classical theories of gravitation. For a survey of current work toward creating a quantum theory of gravitation, see quantum gravity. The early attempts at creating a unified field theory began with the Riemannian geometry of general relativity, and attempted to incorporate electromagnetic fields into a more general geometry, since ordinary Riemannian geometry seemed incapable of expressing the properties of the electromagnetic field. Einstein was not alone in his attempts to unify electromagnetism and gravity; a large number of mathematicians and
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