according to the constitution how can the united states declare war
Declaration of war by the United States For the United States, Article One, Section Eight of the Constitution says "Congress shall have power to ... declare War." However, that passage provides no specific format for what form legislation must have in order to be considered a "declaration of war" nor does the Constitution itself use this term. In the courts, the United States Court of Appeals for the First Circuit, in Doe v. Bush, said: "[T]he text of the October Resolution itself spells out justifications for a war and frames itself as an 'authorization' of such a war."[1] in effect saying an authorization suffices for declaration and what some may view as a formal Congressional "Declaration of War" was not required by the Constitution.
Declaration of war The legality of who is competent to declare war varies between nations and forms of government. In many nations, that power is given to the head of state or sovereign. In other cases, something short of a full declaration of war, such as a letter of marque or a covert operation, may authorise war-like acts by privateers or mercenaries. The official international protocol for declaring war was defined in the Hague Convention (III) of 1907 on the Opening of Hostilities.