Personally I believe you guys are underestimating North Korea, it has improved tremendously in the manner of equipment, troops, tanks, planes, and officers. North Korea has the capability to fight a long term war since their economy is a "war economy" meaning its centered around their military like most communist nations. Also China has proven that it is willing to go to war to ensure North Korea's Sovergienty. North Korea's battle power is centered around a "blitzkrieg" style strategy and has the capability to carry it out. Probably the chief reason the North Korean assualt in the Korean War was stopped was because we had two full divisions based in Japan along with an expiditionary force in South Korea that we used to blunt their offensive. The majority of those forces aren't there anymore, we no longer keep ANY forces in Korea and if we do its small. So North Korea would undoubtably win if they went to war right now.
Where to start replying to this? It's so full of misunderstandings.
Sgtgunn has summed up the military situation well. I'll deal with the rest.
Yes, the North Korean economy is centred around its armed forces. But that doesn't make it capable of supporting them in a war. It's a war economy in peacetime, & it's at full stretch. It depends on foreign aid to stop its population starving. Unlike the peace economies of other countries, it has nothing left to mobilise. What it has is all it's ever going to get. It has no money or credit to pay for any resupply of anything, no rich civilian economy to call on for extra transport, fuel stores or the like - nothing.
You are wrong: the USA does keep forces in Korea. There is a small ground force, & a few USAF squadrons. Those USAF fighters alone are enough to defeat the KPAF rather quickly, but they won't need to do it alone, since they can be reinforced very rapidly by USAF & USN aircraft from Japan. And then there are the S. Korean forces, which you don't even seem to be aware of the existence of.
In 1950, the North Korean armed forces greatly outnumbered those of the South, & were better trained & far better equipped. That is no longer true. The only advantage the North now has is in raw numbers, as Sgtgunn says. Also, again unlike 1950, the South is now enormously richer than the North. It can mobilise its civilian economy to support its armed forces, can afford to import whatever it needs to sustain a war, & can bring it whatever it needs in its own ships, protected by its own navy. On top of that, it will have US help.
China went to war in 1950, at the height of the Cold War, when trade with the USA was nil & the USA was backing a rival Chinese government in Taiwan, which had been finally driven from the Chinese mainland only months before, to keep the US army away from the Chinese border. That proves nothing about China's willingness
now to go to war to protect North Korea's independence. China is a different country now. Its leaders were small children, or not even born, at the time of the Korean War. They're Chinese nationalists, not Communist ideologues. What happened in 1950-53 is no more a guide to Chinese policy now than WW1 was to German-French relations in the 1970s.
I'm not sure what year or century you think this is. You say "eir economy is a "war economy" meaning its centered around their military like most communist nations". What communist nations do you refer to? I can't think of a single other country in the world which fits that description. China? State-dominated capitalism, not communist, & the economy is certainly not centred around the military. And so on.