Answer by Jon Groubert:
Yes and yes. In 1967, a guy took over an abandoned WW II anti-aircraft platform in the middle of the North Sea and declared it to be “Sealand.” In fact, it is the Principality of Sealand, and he issues passports and prints stamps, too, with a flag, and a coat of arms, and everything. As since it is a principality, he also sells royal titles, so you too can become the next Baron of Sealand.
So, that guy has declared an off-shore platform to be a nation. Is that good enough? Well, as an example, on the show The Office, the manager, Michael Scott, played by Steve Carell, walked out among the cubicles of his office, and in a loud, clear voice, said, “I declare bankruptcy.” That’s not good enough – the government has to agree to your declaration. And just like declaring bankruptcy, to actually be a nation, you need to have other nations agree with you by “recognizing” you as a sovereign nation.
But as far as this guy’s concerned, he’s a country. Now, that won’t really matter as long as you don’t make a nuisance of yourself. The guy who declared Sealand has been going strong for almost 50 years now, and no one’s done anything about it. Plenty of countries are younger than that. There is no international police force or army that goes around and shuts down fake countries. He gets to call himself a country, and no one takes the time or effort to do anything about it, and so he continues to be a country after almost 50 years.
On the other hand, declaring war on an actual country is making a nuisance of yourself. Well, only if you actually do something beyond the declaration, something that has some sort of actual physical effect on the country you declared war on. If you do that then, yeah, that country is going to take offense and do something about your “country”.
BUT – as long as you’re just “declaring” a country, and as long as you’re just “declaring” war – in exactly the same sense that Michael Scott did when he “declared” bankruptcy – then yeah, sure, you can declare war on the United States, and no one’s going to stop you.
No one’s going to care, either.