10 USC 161 - Combatant commands: establishment

(a) Unified and Specified Combatant Commands.— 
With the advice and assistance of the Chairman of the Joint Chiefs of Staff, the President, through the Secretary of Defense, shall
(1) establish unified combatant commands and specified combatant commands to perform military missions; and
(2) prescribe the force structure of those commands.
(b) Periodic Review.— 

(1) The Chairman periodically (and not less often than every two years) shall
(A) review the missions, responsibilities (including geographic boundaries), and force structure of each combatant command; and
(B) recommend to the President, through the Secretary of Defense, any changes to such missions, responsibilities, and force structures as may be necessary.
(2) Except during time of hostilities or imminent threat of hostilities, the President shall notify Congress not more than 60 days after
(A) establishing a new combatant command; or
(B) significantly revising the missions, responsibilities, or force structure of an existing combatant command.
(c) Definitions.— 
In this chapter:
(1) The term unified combatant command means a military command which has broad, continuing missions and which is composed of forces from two or more military departments.
(2) The term specified combatant command means a military command which has broad, continuing missions and which is normally composed of forces from a single military department.
(3) The term combatant command means a unified combatant command or a specified combatant command.