Well, I had to do some research to freshen my memory, but I think I've got an answer now.
An important thing to mention now, is that you HAVE to look into the foreign relationships of the superpowers of the world to get a good idea of how different countries will most likely react to certain events. Ok, let's begin!
Note: I'll establish now that WWIII is going to a blood bath of biblical proportions.
Now, we all know relationships between North and South Korea are very poor, with trade between both countries being completely cut off as of 2010. South Korea's allies are currently the US and some nations in Europe. Canada and other countries involved in UN disputes also have close ties. North Koreas primary ally is China, who has close ties with Russia, although it is seeking diplomatic relations with all nations (China's goal is generally the preservation and creation of peace). These relations include South Korea and more recently India, despite their rough history. In fact, China has solved many of it's disputes with its border countries (hint border, so not Japan for obvious reasons). But I'm Rambling here, so I'll move on.
So, Russia isn't technically allied with China, but they have signed an agreement saying that Russia would sell their oil and military "advice and technology" for a chance to employ their people, and China would grow economically and increase its stance on the Republic of China (Taiwan).
Also, European/American continent support for Israel, anti-terrorism and so on.
Now, the most likely case is North Korea will go to war with South Korea (again) to unify the peninsula and finally claim it their own. Both countries have a grudge for Japan for its treatment of their people during WWII. Now, the US would immediately deploy to back up the South, while China "may" get caught in the middle but eventually join the North. That is, if it doesn't go to war to claim Taiwan or other land claims.
Russia would have sold its military equipment and expertise, and also fuel by now, so China would be a new superpower, rivalling even the US. Many countries would be forced to pick sides to avoid conflict with either powers (except switzerland because they're ALWAYS Neutral).
It would start bloody, and get worse as time goes by. Casualties would be high on both sides and tensions would grow to dangerous levels. I'd predict Nuclear weapons would be the last to be used, though anything could happen. Since the Horrors of war are still fresh in our minds, Leaders all over the world would try to come to an agreement. Whether this would work or not is not sure.
Best Case scenario: All countries sign a cease fire, and try to solve problems via political means. Also assess damages and costs, etc.
Worst Case Scenario: The war wouldn't end until either one side prevails, or all countries push the Nuke buttons, destroying all life as we know it.
One thing I know for sure is that it's going to be a very long, bloody battle, that will make WWII look like a game of cat and mouse. The horrors we know now, would be minuscule compared to the atrocities that would be committed during this next Great War. Our only hope is people will awake from their insane dreams, and try to right the wrongs done in the past, to avoid a fatal future.