"We" won´t declare it, they will! When they fear the civilians may revolt for various reason, hyper inflation bringing about lack of food, some disaster, Aliens popping up and saying "hello". Anything which might threaten the status quo and the NWO dominence of the world.
Civilisation is bound by law and when people stop fearing the consquences of police men coming to arrest you they do things like rape, loot and graffiti. This is when your ordinary police are replaced by guys with assault rifles and flamethrowers riding tanks into your area
Because we'd get help from the National Guard and the Coast Guard before we'd resort to Martial Law.
And if some country ever actually "invades" us then nothing good would come of that and they know it. And I'm not talking about invading Hawaii or Alaska. I mean the actual United States that is.
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Have you lost your mind? Tell me where you think we crossed the line. No more drugs for me, pussy and religion is all I need.