What does North Korea want? The same thing every country wants and that is self-sufficiency without having to sell their non-reproducible assets (mineral wealth) to achieve it. In order to achieve this, they must reunite with South Korea which has the reproducible wealth in the form of its agriculture.
The Soviet Union wangled its way into the Pacific war with Japan, contributed little, if anthing to the end the conflict and stupidly the United States agreed to give hegemony of the northern half of what was a united country to the Soviet Union who in turn abandoned it to the Chinese. The north attempted to unite the country in the early 1950s but were thwarted by our presence and stupid strategy of attempting to reinstate the unnatural status quo. Neither side gave up their attempt to reunite the country and the only reason the North is threatening us is because of our support of the government of South Korea.
North Korea is not a threat to invade the United States. Like ISIS, the Taliban, Al Kaida and the Irish Republican Army they commit terrorist acts in order to get us to mind our own business and allow them to fight their real enemy be it Sunni, Shiite, or the Irish Republic. It is the later civil war that the British intervened in which prevented the Catholics and the Protestant Irish to settle their dispute and brought terrorism to Britain, just as our intervention in Israel has brought terrorism from both Sunni and Shiites on the U. S. and countries that actively support Israel.
The obvious solution is to pull our troops from South Korea and let the Koreans figure out how to settle any argument between the North and South just as the Southern States did with the North in our own civil war. That dispute had nothing to do with slavery but was a battle between those who wanted to retain States rights and those who wanted a strong central government. The Swiss settled this issue centuries ago when they decided on federation with the Cantons, retaining essential autonomy from a central authority. We would have done well to follow their example. The framers designed such a federal republic with the original Constitution but the greed of those who wanted a strong central government emasculated the pact starting with the very first Congress.
None of this makes very much difference because overpopulation is rapidly outpacing natures ability, even with human intervention, to feed the growing population. It has occurred already in many countries who have neither the agriculture to support their populations or the assets to purchase it from those who have a surplus. It has already started here, being saved only by massive welfare that still leaves many behind. It is exacerbated by an economic system that distributes natures wealth unevenly through the government tax system.
If you read my two books, The Real Economy and the Constitution, a Document Steeped in History and a Compromise Devoid of Promise, you will understand what it is that the politicians did and how they did.