South Korean military intelligence analysts believe that North Korea, despite spending about 90 percent less than South Korea on its armed forces, has turned itself into a very dangerous threat to South Korea. The north has done this by concentrating on a few offensive weapons and creating the capability to launch a devastating initial attack, but with not much to follow up with or defend North Korea with.
The offensive threat comes from a few crude (so far) nuclear bombs, Cold War era chemical weapons and lots of artillery. North Korea could not win a war with this type of force, but because Seoul (the southern capital where half the population and a quarter of the GDP are) is so close to the border, North Korea has lots of targets within range of rockets and artillery. Sprawling Seoul is 40-50 kilometers from the North Korean border. The city alone is 600 square kilometers, and the suburbs are even larger. There are over 17,000 people per square kilometer (45,000 per square mile) in the city.
The southerners know the north is desperate and heavily armed. What do you do? South Korea has responded by increasing its ability to quickly halt any rocket and artillery bombardment from the north. This would involve a lot of accurate South Korean artillery fire and smart bomb use in a short time. Many North Korean targets would be destroyed but the south has much more to lose, even if the northern attack is cut short. Moreover it is no secret what the plans of both Koreas are, but many of the details are kept out of sight and, as the old saying goes, “the devil is in the details.”
One of the well known facts is that some 70 percent of North Korean ground forces are within a hundred kilometers of the DMZ (Demilitarized Zone, the border with the south.) This was long the main threat to South Korea but since the 1990s growing shortages of money, fuel and food shortages have greatly reduced North Korean Army capabilities. Two decades of extreme poverty have done even more damage to the navy and air force. So North Korea quietly shifted their strategy.
The Inmun Gun (the North Korean armed forces) looks scary on paper, in large part because nearly every adult male serves at least six years in the military. The big problem is that years of economic problems and failed harvests have left the troops poorly equipped, often hungry and increasingly insubordinate. With most of the best educated troops bribing their way into any job but one in a combat unit it is increasingly doubtful if the North Korean combat forces could get very far during an invasion of South Korea. Despite all that a lot of North Korean troops are believed to be reliable enough to carry out orders to make an initial attack on South Korea, an effort that could end up doing a lot of damage. The North Koreans hope that would cause enough disorder in the south to allow the threadbare Inmun Gun to advance through the DMZ (via a few corridors cleared of mines) and move into the south and eventually induce the south to ask for peace on terms favorable to the north. Even China and Russia consider this a dangerous fantasy but the north has proceeded with their plan and that scares everyone.