Constitution Art I Sec 8
The Congress shall have Power
To provide for calling forth the Militia to execute the Laws of the Union, suppress Insurrections and repel Invasions;
Art I Sec 10
No State shall, without the Consent of Congress, lay any Duty of Tonnage, keep Troops, or Ships of War in time of Peace, enter into any Agreement or Compact with another State, or with a foreign Power, or engage in War, unless actually invaded, or in such imminent Danger as will not admit of delay.