The United States Constitution states, “The Congress shall have Power . . . To declare War…" However, recent history has shown that this clause for all intents and purposes is null and void, because the wars that America has had against Korea, Vietnam, Iraq, and Afghanistan, were all wars that were not authorized, declared, nor approved by Congress. On the other hand, on December 7, 1941, a day that will live on in infamy, in which Pearl Harbor was attacked by Japan; on the very next day, FDR went in front of Congress to ask for a declaration of war, which was thereupon authorized by that Congress that same day. This so signifies, that if the President is willing to ask for a declaration of war, that the Congress, the only branch of government authorized to declare war, will vote upon it.
The main reasons why Presidents no longer bother going to Congress to get a war authorization, is that the President, first and foremost, recognizes that the President, based on recent history doesn't actually need to get authorization, despite what the Constitution stipulates, and further, that the President will not be held accountable for having not done so; and additionally, the President is just one person, and therefore the technology-military-industrial complex obviously prefers to just have to convince or coerce one person to make war, rather than to be involved in an actual debate with the representatives of the people, that may or may not be so eager to authorized a formal Congressional declaration of war.
The unfortunate thing is that when a Constitutional republic devolves into an Imperial Presidency, then that country is functionally not adhering to its own Constitution, so that the voice of the people is effectively negated. Further, wars are the very thing that the people should have their say upon, for it is their blood, their money, their safety, and their reputation that is put at stake, in which, no President, on the say-so of that President, should be able to simply declare war without such being reasonably debated and vetted by the people's Congressional representatives.
The Declaration of Independence states that "…a decent respect to the opinions of mankind requires that they should declare the causes…" for that independence, and the Declaration of Independence, then proceeds to do that very thing; along with the salient fact that the Declaration of Independence is signed by at least one representative of all of the thirteen colonies at the time of its declaration. The reason that this is so important is that the signatories to that Declaration pledged their lives, their fortunes, and their sacred honor to that document.
This so signifies, that any war declaration made by the Presidency without the expressed authorization by Congress, is contrary to the highest law of this land, which is the Constitution, and that circumventing such is inimical to that Constitution. The declaration of war is one of those decisions, that has major and significant consequences, so that, it should be accorded the type of respect that permits the members of Congress to debate the merits of, and should be done in a manner in which the people are an integral part of such decisions, for when war comes, it is the people's blood and the people's children that will do the fighting, the killing, and the dying.