This will never happen for a variety of reasons;
First of all, South Korea would not join with North Korea without them first abandoning their "Communist" ideas. North Korea, with what the current and future leadership looks like would never do this. Kim Jong Ill and whoever replaces him (his son, which one I'm not sure) love having Godlike power over their people and are not going to give it up. This means North Korea would have to invade South Korea to take power and that's a war they cannot win. North Korea invades through the DMZ, basically a giant mine field leading towards machine guns = many NK troops dead. Then they will break through and by that time the U.S. and South Korean forces will be pulling back to more defensive locations abandoning the "speed bump" bases closer to the north. While this looks like a retreat, it isn't. While their doing this USAF B-52 bombers will be being deployed from Barksdale AFB and other bases alongside F-16 and F-22 fighter escorts, many already located in Japan. These fighter jets join their Jappanesse and South Korean collegues and slaughter the North Korean Air Force (if there is one) while the three Naval forces alongside other allied navies (United Kingdom, Australia, Canada, the list goes on and on) bombard the invading North Korean troops while turning the North Korean surface fleet into a submarine fleet. About twelve to fourteen hours later the B-52s arrive and release their payloads over the DMZ cutting the invading North Korean troops numbers in half.
Now that the invading NK troops are being bombed into submission by the bombers remember those U.S. and South Korean troops that retreated south, well, their advancing now towards the scattered and terrified North Korean invasion force. The NK soldier has been told the North Korean army is invincible and will conquer all who stand before it. He believed this, but then his friends stepped on landmine after landmine, were torn limb from limb by machine gun fire and then the bombs started to drop. I picked the B-52 for a reason, their payloads are massive even compaired to the B-1B and Stealth bomber, they are the USAF's heavy bomber and there are a lot of them. Now, the North Korean soldier is learning he can be defeated and the well fed, rested and unbombed U.S. and South Korean troops are advancing north, aided by Marines from the United States, Japan, Great Britain, Australia and other nations from the east and possibly west. Within one week the North Korean invasion force will have surrendered and Kim Jong Ill will be cowering in Pyongyang waiting for, if he's lucky merciful U.S. troops, or if he's unlucky, angry South Korean or Jappanesse troops.
Well, let's say Kim figures what I just said is what would happen when he sends his invasion force south. We'll assume he has a nuclear weapon and he decides to soften up his enemy first, perhaps force them to surrender to his great self through use of the nuclear bomb. He fires at the U.S./South Korean base near the North Korean border and the weapon is a success. With that large base gone he sends his invasion force south to victory, right. Wrong. If North Korea fired a nuclear weapon at South Korea and especially if it worked he would have less than an hour left on the face of this Earth. Deploying a nuclear weapon is serious buisiness and if he did so the U.S. would have no other option but to retaliate in kind and fire on Pyongyang with one of the weapons from the U.S. stockpile. Kim might have a nuke, but I can guarantee you it is nothing compaired to a modern U.S. nuclear weapon. 5, 10, 15 megatons of nuclear annihalation would hit his capital and in less than an hour the Second Korean War would be over in a flash of horrid white light.
Second, this is according to a recent article I read a week or two ago. Apparently, due to economic reasons and the devaluing of North Korean money affecting the people's savings (they do have them), the people are starting to love their dear leader less and less. Kim could order his people to war and face a rebellion, possibly even a military coup by officers smart enough to know their great leader is sending them to their deaths for nothing better than his ego. There is even a chance that North Korean troops could break through to South Korea and surrender to the first South Korean soldier, American soldier or even reporter or buisinessman they find to escape their "Worker's Paradise."
Third, China would not want to work with North Korea, in fact, they could join the South Korea, U.S. and Japan in fighting against the North. Think about it, attacking U.S. forces especially is economic suicide, they know that. Who buys all their cheap crap, the U.S. Also, while the Chinesse leadership want more power, they don't want to share it with a lunatic like Kim Jong Ill. They know a war with a still strong west is suicide as even a near billion man army is no match for bomber fleets, long range missles and selective bombing. Plus, they need to keep their people working, busy people don't complain. Anyway, when China makes their move for power, they aren't going to need North Korea nor want it.
And finally, invading the United States is nearly impossible for a country like North Korea, China, or even all of Asia. The U.S. is stable and has the Pacific ocean in between it and Asia. There are only two ways this Asian army could get to America, by sea or by air. They haven't got the aircraft to get that many troops to the U.S. and if they did American and NATO fighter pilots would have a field day shooting them all down. It'd be less a military action and more of a massacre. If they came by sea, well, more of the same. The U.S. Navy and the other NATO navies would sink their fleets no problem. Destroyers, submarines and fighters would make quick work of their naval fleets. And even if they could reach the United States, we still have the United States military, the police AND the armed PUBLIC. There is an old quote by a Jappanesse admiral that basically says it is impossible to invade the United States as there would be a rifle behind every blade of grass. Gun ownership in the United States is high, and I don't mean shotguns and handguns. Semi-Automatic rifles like the AR-15 (Semi-auot M16), Steyrs (semi-auto AUGs), AK clones and the list goes on and on. All of those publically held semi-automatic firearms guarantee this nation can not be invaded as the American people could carry out an insurgency that would overpower any military.
While the situation is basically impossible this game still looks interesting. I'm going to go and see what else I can find out about it. If it's coming out on the PS3 maybe I'll pick up a copy.
