It used to be that for the US to declare war—it took an act of Congress. To be more precise, by the authority of We the People, Article 1, Section 8 of the US Constitution, Congress is given the exclusive power to declare war; and this means that an elected body of 535 people must pass the declaration with a simple majority.
Excerpt of the Constitution for the United States of America.
After America entered into the Kellogg–Briand Pact in 1928, the US didn't declare another war until World War II, and it hasn't declared war since. I think most people would see WW2 as an exception to the rule. After all, America's declaration followed Hitler's, so in effect, it was more of a proclamation of self-defense as opposed to a declaration of war. In short, the US didn't start the fight. They finished it. By they, I mean, mostly Russia. And This is why Russia has an annual victory day celebration; it's because, by and large, they earned that particular victory.
Following the second world war, the aforementioned-pact helped to create the legal framework for crimes against peace. And it was for committing these crimes that high-ranking Axis leaders were tried and executed following both the Nuremberg and Tokyo tribunals. After the Kellogg–Briand Pact and the events that followed, it should suffice to say that anyone who conspires to start a war of aggression is now subjecting themselves to Nuremberg Principles. Said offenders can, in theory, be found guilty of violating international law and punished accordingly.
Screenshot: Google Books, Author: Kelly Dawn Askin
The above should highlight why our dear leaders in Congress have all but abandoned this outdated notion of declaring war. Technically speaking, America hasn't prosecuted a war since WW2 because it's against international law to wage wars of aggression. That said, what's a bloodthirsty nation-state to do? It's quite simple, you do an end-run around the word "WAR" and call it something else. This way, it makes it impossible to violate the rule.
Vietnam is a good example. That wasn't a war—it was just a military conflict. Not only do the elected scumbags in government maintain a straight face while playing these word games. It now appears that someone would like you to forget that Congress has forever ceded its constitutional authority to wage war over to a sole decider, one who just so happens in this case, to be a demented puppet of the deep state establishment. Yes, you've read that correctly; Sometime between 01/17 and 01/29 of 2021, the good folks who run the Senate.gov website saw it fit to remove the page entitled 'Official Declarations of War by Congress'.
senate.gov
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Origins_WarPowers.htm
WarDeclarationsbyCongress.htm
You see, somebody wants you to forget that such a thing ever existed. As memory recalls, it was Dr. Ron Paul who harped on this point over and over again. It must have been like Chinese water torture for the military industry, Congress, and their lawyers, that and his use of the term wars of aggression, which by their very definition are war crimes in and of themselves.
I reckon that some slimy lawyer or politician saw Ron Paul's unfortunate stroke last year, figured that he's on his way out, and summarily decided that now is a good time to permanently shit-can that pesky notion of declaring war. Either that or perhaps Biden and co. plan on unilaterally starting a new war. What if this new war gets waged on the American people? Would that make the topic of who gets to decide these things a bit more interesting?
Odd factoid: The last country that America declared war on was Romania (still at the Senate site):
https://www.senate.gov/artandhistory/history/common/image/HJRes321_WWII_Rumania.htm
Ahh, that makes sense. Romania is one of the Axis powers. They committed more troops than the other Axis powers combined, save for that of Germany. Supposedly they were in an ass-kissing contest with Hungary to see who could impress Hitler more. I guess that's why they got on America's shitlist.