I'm just going to point out that even a war isn't a binary choice where one nation must be eradicated.
If USA or any NATO country is attacked NATO can just beat back the attacker and force them to accept peace (and probably some heavy sanctions starting with reducing their military.)
Granted that USA seems to think otherwise. Iraq and Afghanistan were bombed back to stone age. Afghan specifically tried to surrender but US military went with "LOL nope, we want more blood" and continued fighting the war long after one side was waving the white flag.
https://theintercept.com/2017/08/22/afghanistan-donald-trump-taliban-surrender-here-we-are/
Now, had the surrender been accepted would that have somehow been worse for USA? I mean it would have meant less deaths all around. Less dead US military personnel, less dead Taliban and a lot less dead civilians. They could have kept on hunting Osama even without a war going on. Less money would have been needed for the rebuilding phase for certain.
This is not some video game where the war isn't over until every enemy unit has been shot. In fact, if USA showing up on their doorstep is enough to stop someone from invading a US ally isn't that a good thing? "Oh wait, you were serious about that NATO stuff? Ooopsy daisy, we'll just go back home, ok?" Huzzah! Medals for everyone! Let the diplomats handle the remaining issues.
With all due respect, while true, all of this is really only tangential to the main argument here. First of all, if North Korea does attack the United States or its allies (and for the record, I don't think they would*), it's not going to be with a conventional strike. It's not going to be with a land invasion. I would say by far the two most likely scenarios that
do involve North Korea initiating aggressive war would both be nuclear strikes, either on Japan or on US territory in the Pacific Islands (or god forbid, the West Coast.) In either of those two scenarios, there is no turning back. There is no trying to find a peace deal, and I would expect our nation to react to a nuclear strike in kind - especially since living in a prominent state capitol on the West Coast of the US, I'm a potential target (if a low probability one).
The other big factor here is deterrence. The principle of deterrence demands that we show North Korea, even if it's not true, that we are not only capable, but ready and willing to launch a massive retaliatory strike on North Korea if they choose to spark an open conflict -
especially a nuclear conflict. Trump, for all his uncountable faults, is at least capable of sounding like he's ready and willing to retaliate (probably because he is). This sort of speech is exactly what you would want to say if you want to loom over North Korea and let them know that if they throw a bomb at a US country, their ass is grass. Which is, I believe (I hope), the main point of all this bluster.
*: Honestly, I should probably mention that I don't think North Korea will ever actually spark a war themselves. They know the position they're in, they're not stupid, and Kim Jong Un's biggest goal isn't to eradicate the US or Japan, it's to stay in power, and staying in power involves not stabbing sleeping dragons in the eye. I think North Korea's end goal here is just internationally recognized independence with the Kim family in control, and they're not about to risk that. However, the caveat we're discussing here is "if North Korea attacks the US or allies", and so I have to discuss it with that in mind - even if it's an outside possibility.