North Korea threatened specific bases in Japan and Guam

North Korea has been pretty much the only one to make actual threats in a long ass time. The reason nobody does anything is because they don't have anything we need and they aren't a large enough threat to anybody.

An under developed country with a desperate need to refresh its infrastructure, economics and re-educate its people? Sounds like a business paradise to me. Even though ultimately SK will have the most legitimate claim to NK's land, it still provides mouth watering possibilities into the advantages that most businesses can take in this land of beginning. There aren't that many places in the world where one can go in and develop things from almost scratch.

Though it is highly unlikely that NK will be flattened for rebuild. SK will want to take over NK to end the divide, but they need a lot of help to do that... China wouldn't want that to happen, because in order to invade NK, it would be strategically beneficial to place a land invasion force near the flatter part of NK (the western side), meaning China will have to provide some space for the US to build new base of attack of some sort on their land, which forces them to co-operate with and open to the US - a stupid move diplomatic wise. Not to mention a war against NK will further hurt the US economy, doing no good to China's finance. Also China certainly doesn't want nuclear missiles targeting its own cities. The Russians will bathe at the idea with an American base next to their door step spying whatever they have going on secretly in Sibera, not to mention they will no longer be able to ninja some stuff to NK for a quick buck. Japan doesn't want SK to expand, but it does not have any legitimate claim to NK's resources, so the most it will do is to defend itself and provide backup support for US troops.

Even though a war does break out, it would have a fast beginning, but slow progress thereafter. The eastern part of the country will be where most of the NK army retreat to after pyongyang eventually falls. Even though the weather is unforgiving, you would think the vast tunnels in the mountainous area would be able to sustain the regime for years to come... so the whole thing might turn out to be another Iraq invasion.