I try not to panic when North Korea does a bit of saber rattling. The difference right now is that they may actually have a saber to rattle. The intelligence briefings don't come across my desk, but it appears they could have missile ready nukes. About twenty years ago under the Bush administration it looked like we could have had a diplomatic solution, but that never came to pass. Now we are stuck with the fallout from that failure. Maybe real fallout.
US options are pretty limited right now. Economic sanctions have not worked. It's not like North Korea was ever tightly connected to the world's economy in the first place. Apparently Kim has even managed to somewhat improve the economy since he came into power.
So what does the US do? We sail a few aircraft carriers off the coast. Some bombers fly around a bit. Sometimes troops and equipment in South Korea get shuffled about, like chess pieces that never threaten the king. After decades of this the North can't take the threat all that seriously, can they? While all this was going on, the North Koreans were testing atomic weapons and mastering missile technology.
It doesn't look like a diplomatic solution is likely. In fact, the Trump administration has cut funding in that area. Trump himself has upped the rhetoric and seems to be cribbing Kim's “Death to all” vocabulary. So that's a change from the past. Where will it lead? Will Kim assume that Trump is just blowing smoke and ignore him? That would make the President look weak.
One option is for Kim to launch an attack on US assets. He's threatened US cities and the US base at Guam. I'm not sure about the North being able to hit US cities, but an attack on Guam is definitely within their capabilities. What happens after that is anyone's guess. However, I don't think it will end with the US taking its lumps and backing off.
That would be just the excuse Trump and the military needs to attack North Korea. The United States could decide that Kim's nukes have to go and attack the nuclear facilities. One handy thing about attacking nuclear weapon production areas, the US could even use tactical nukes and claim the radiation is from the North's nuclear program. Don't tell me they haven't thought of that.
Don't think the US would never attack first. We do it all time. If Trump feels threatened by a possible impeachment, a good little war would be the perfect distraction. One cannot rule out the possibility.
So how does this end? It will be a quick little war and everyone would be home before Christmas. Wait, no, that was WWI. That didn't turn out so well either. China and Russia would not be happy with a nasty little war right on their doorstep. Last time that happened a zillion Chinese “volunteers” swarmed across the border.
South Korea would suffer greatly. Their capital is within heavy artillery range of the North. It doesn't even take high tech weapons to devastate the country. Their military, while smaller than that of the North, is better equipped and trained. Then there is the little issue of US troops on the ground. Our men and women would be involved from day one.
Japan would probably get involved. North Korea threatens them all the time too. They are pretty close geographically, so there would be plenty of opportunity for conflict. In recent years Japan has been strengthening their military and quietly flexing their muscles. The official pacifism of the post WWII years has steadily eroded.
If I had to bet, my guess would be that any sort of military action would quickly or eventually spiral out of control into a greater conflict. Millions would die.
If you are prepper, your very last get out of Dodge moment will be when military action starts. If you are lucky you'll have enough time to leave the cities. However, if the first attack is on a major US city, then forget about it. Transportation out of all major cities would soon gridlock. If you are lucky your warning will be either something like a North Korean attack on Guam, or a US surgical strike on Kim's nukes. That might give you enough of a head start.
One thing for sure is that situation is not going to remain static. Something is going to happen. Cooler heads and diplomacy? Yeah, that would be nice.