1. The Japanese announce that in response to NK they will produce nuclear weapons.
2. The Americans announce that #1 is understandable and that they will be fast tracking a Japanese request to purchase plans for light weight nuclear warheads, the Pershing II missile system, and Tomahawk cruise missiles.
3. Through back channels, the U.S. and Japanese tell the Chinese (and Russians) that they are willing to turn their plans off IF North Korea is dealt with.
Throw the ball to China and they will jerk the leash on NK pronto. They have no desire to have a nuclear armed Japan.
The real decision maker is China. If we are serious about NK then we should look to China's pressure points.
In fact, I would approach the Chinese with an offer to encourage them to invade NK as a humanitarian move. In return, we would agree to not base U.S. forces on unified Korean soil. Let the Chinese occupy NK and try to make some sense of that mess, while keeping the DMZ in place. After a decade or so, the Chinese will be ready to turn the mess over to South Korea.
None of which would work.
Curious you mentioned the Japanese. As it happens it’s the Souks that have the most to lose if the Norks get frisky. And just yesterday the Chicoms had a pretty detailed news story about the Souks explaining some of their capability. They just shot off a surface polaris style missile and a sub launched cruise missile in plain view of the Norks complete with a highly visible Israeli style bunker hit. The South guy was carefully explaining how they could put their missiles thru any particular office window in Norkland. I’m guessing the Souks have figured out they can’t depend on Obamuzzie on any particular day so they are willing to light it up if they get spooked———and they have some really good matches.