North Korea is actually quite limited in terms of what conventional military actions it can take. Since it was set up as a puppet state, the number one priority of the regime has been its own self-preservation. If North Korea were to invade the South they would lose and lose badly. South Korea would suffer heavy casualties, but they would prevail. Here’s how I would see it playing out:
North Korea can’t simply invade across the 38th parallel. It’s too heavily fortified. Their only option would be to launch artillery shells at outer islands, or attempt an amphibious landing on the mainland of South Korea. The only problem is that they have very limited capabilities on the water and in the air.
Naval power can be described by three different categories: Blue water Navy, Green water Navy and Brown water Navy. A blue water navy is able to operate thousands of miles from home, deploy for long periods of time, and usually has carrier groups, submarines, missile, amphibious landing, and air strike capabilities. The United States is the most obvious example, with Japan, France and the UK being the others. A green water navy is able to operate within its sphere of influence, but is unable to extend more than 2,000 miles from home for long periods of time. Examples of this would be South Korea, Germany, China, Turkey, India, Australia, and Russia. A brown water navy has the capability to patrol its own territorial waters, but not much beyond that. This is where North Korea falls in. The North Korean navy is divided into two fleets, east and west. However, they are unable to train alongside one another because neither one can go the distance around the Korean peninsula.
Next is North Korea’s air force. On paper they have 800 jets, but I doubt that even ½ are operational. All of their equipment is outdated back to the 60’s (70’s at best). Of their total air fleet, how many have been cannibalized for spare parts? Then there’s the issue of pilot training. In South Korea, Japan, the US, and most of our European allies; fighter pilots receive about 200 hours of flight time per year. In North Korea, their pilots are lucky to get twelve. Fuel would also be an issue. If North Korean pilots are limited to twelve hours per year due to fuel shortages, they can’t possibly be prepared for protracted air combat.
That leaves the land force, which is the most dangerous. North Korean equipment may be outdated, its soldiers poorly trained and malnourished, but they still have thousands of artillery shells that could reach Seoul within a matter of minutes. This is the only card they have to play, and they can only play it once. After that, it’s game over. Almost simultaneously, the US and South Korea would launch a massive counterattack. The first wave would be primarily with cruise missiles, taking out the artillery, anti-aircraft defenses, and air fields to establish air supremacy. Next we would use fighter jets and medium range bombers to take out the roads and rail lines leading to the DMZ, and lines of communication and transportation leading to the capital. This would leave North Korea’s army sitting ducks on their side of the DMZ.
This would not take very long. It would probably be over with in less than five days, but there would be heavy casualties on both sides. There is still the possibility that North Korea has sleeper agents in the South. That will cause problems, but South Korea is probably prepared for that. It’s unlikely that China would back North Korea if they were to launch an attack. China’s not the same country it was in 1950, and Chinese investments & trade with South Korea is greater than the entire North Korean economy, not to mention China’s level of trade with the US. As much as China dreads the notion of an influx of North Korean refugees that would come about as the result of a war; the greatest fear of the Chinese leadership is an insurrection within their own country (back to governments and self-preservation) and the quickest way to bring that about would be a major economic upheaval, which is what would happen if China’s economic relationship with South Korea, Japan and the US were in jeopardy.
In China, provincial governments have borrowed money from the Central Bank of China to the tune of $4 trillion in order to build skyscrapers, expressways, subways, high-speed rail, power plants, etc. The Central Bank of China purchases US Savings Bonds and Treasury Bills to build up foreign capital. If their economic ties to the US were at risk, they could easily be looking at a major economic crisis. The Chinese people will not stand for that, and the leadership in Beijing knows this. At this point they see North Korea as an embarrassment to their diplomatic efforts and to their credibility as a major player on the international stage. For that reason, I think the reaction by China is the one to watch at this point.