Throughout US history, although the US has participated in upwards of 200 armed conflicts of various descriptions, the Regress has only declared war 5 times. If not mistaken, these were: War of 1812, War of Northern Aggression, Spanish-American War, WW I, WW II. The Regress, in all its political posturing, couldn't even be bothered to declare war against Iraq in 1990-1991.
The argument that there is no state of war because the Regress hasn't declared war is historically fatuous at best.
Actually, war was declared quite a few times more. Even in dealing with the Barbary Pirates, war was declared. Only in some of the Indian actions was war not declared. War was declared in both Mexican Wars. A better statement would have been, since WW2, Congress has declared war only once: Gulf 1.