Both North Korea and South Korea want to conquer the other territory, and both would do so inflicting as little harm as possible to the other side during the process. In the 1960s North Korea had little to gain by conquering the South, by the 1970s both North Koreans and South Koreans had been brainwashed long enough to hate each other, both sides confessing to me that they saw no humanity in the other side. The 1980s were a time when North Korea tried to make a few moves to conquer the South, first because of the power vaccuum South president Park Jung Hee's assassination had left. Second because of the growing resentmemnt of their own government by the South Koreans, as South Korean troops shot and massacred South Koreans in Gwangju, and mass protests by South Koreans against their own government were met with violent repression. US-South Korea relations also soured in 1987, when South Korea did not want the US meddling with South Korean protests, going as far as asking the US media not to report the mass demonstrations.

During the 1980s, the North tried to get the South to fold by perpetrating several terrorist attacks, hoping the South would retaliate with a full-scale invasion attempt, which would lead to a defensive war by the North. North Korea knows what it's doing: don't attack first (in military jargon it is said that it is best avoided to attack strong armies) and then defend against the South's attack, and push back the defense all the way to the very end of South Korea before conquering the territory. The North knows that it would get Chinese help defending for a simple reason: if the North collapses or is under a sea of fire, millions of North Koreans would shelter in China.

Now in 2017 the North is still doing the same: inviting the South to attack in order to fight a defensive war. The idea of a defensive war is simple: put several lines of ground forces along the territory and try to push the ground forces forward. Use the air force or the naval forces if necessary, use missiles if necessary, but try not to destroy the enemy's land, because the aim is to conquer territory. The North knows all too well that over the last few years South Koreans refer to their own South Korea as “hell Jeoson” (hell Korea) and “Tae Han Mang Gook” (the great republic of failed Korea). North Koreans know the dissatisfaction of the South Koreans with their own government, excessive bureaucracy and a nation where bullying is a national passtime. In the meantime, the North is hinting that if it is not attacked immediately that means time to develop other weapons of mass destruction.

The solution: don't give in to the North's invitation to attack. But that is kind of difficult. The North knows that by conquering it would get quite a lot of gems, in real estate, technology, agriculture and other sectors. The North also knows that the South's position shifted to empathy with their brothers in the North over the years. An empathy that is not shared in North Korea toward their South Koreans genetic other half.