They declared war on us formally the week Japan bombed Pearl Harbor, and started sinking our ships.
So if tomorrow Namibia formally declared war on the United States without any subsequent military action, you would advocate invading and overthrowing the government of Namibia just because of their "formal declaration of war"?
What if Germany had not sunk any ships or declared war on the United States, you would have supported letting Hitler do his thing?
Well, sure! That's what we were trying so hard to do, stay out of BOTH world wars. We didn't get dragged into WWI until 1917 (the Zimmerman telegram, that functioned as another German declaration of war, to an outraged America public -- Germany offered to help Mexico reconquer three Southwest America states if they would distract us from WWI: whoops, we found out). We didn't get dragged into WWII until December of 1941, very late.
The fact that we cannot stay out of world wars, that everyone conspires to drag us in because we're so big and powerful and rich is why after WWII we started this "world policeman" role with forward power projection foreign bases everywhere. We are committed to stopping world wars before they start, is the idea. It was a good idea for a long time. Obviously that has not been working out lately: we've been starting wars, not stopping them. Any country that wildly starts wars everywhere runs a real danger of being viewed as a rabid dog that nations of the world have to band together to shoot down -- like Germany was viewed (accurately) under both the Kaiser and later, Hitler.
All the same, you make a good point about Namibia. That's why I added "and started sinking our ships" to the Hitler declaration of war. They have to be able to do something about it, and also, they have to ACTUALLY do something about it or their "declaration of war" need not be taken seriously. Obviously Germany was a powerful enemy: we barely won, twice.
Right now both North Korea and Iran have current declarations of war operative against us. NK has been in a state of war for decades and frequently reiterates it. But they don't actually do much, and not against us, wisely. It wouldn't take much, frankly.
Iran regularly says they want to kill all Americans, nuke us, make war on us, etc. etc., and though the speakers are at a high government level, they don't actually DO anything. Again, wisely, because that situation is on a knife edge. Iran has already declared war against us and against Israel. If they suddenly start sinking ships, we would be actually at war with them. A declaration is not enough, you are right. Talk is cheap, but sinking ships matters.
Note that our shelling Syria would be from ships, not from the air, as we did twice against Libya. I see trouble coming. Sunk ships are our
normal entry into war: that's why Osama bin Laden, desperate to get our attention, hit the U.S.S. Cole. We still didn't pay attention, because he was not attached to a state. But the faked Tonkin Gulf attack on our ship and the faked Spanish attack on the U.S.S. Maine in Havana harbor, and the real German attacks on our shipping, and the real Japanese attacks on our ships at Pearl Harbor --- all those attacks got us into war. It's not the only way, but sunk ships are the usual way to get us into war, and sometimes it's a simple lie by our own government.
I think those American warships are out there to play sitting ducks to get us into a war with Iran.