I've heard things at our school about a possible WWIII. There are several scenarios which can trigger a possible third world war, and the most conflict that's most likely to cause this war would probably be the North/South Korean thing. However, I don't believe that it'll become US vs NK, but rather US vs China. China has always been supportive of North Korea in some way or form, as seen in the Korean War (which is technically still going on as a treaty has never been signed to end it; it's just on a very long cease-fire on both sides). If the US were to release missiles or declare war on North Korea, it would be very likely for China to come in and assist North Korea. And then they get all their allies together, and voila... WWIII.
You have to remember that the first two world wars were started as conflicts between two states, but because of complicated alliances made between countries to protect each other, we ended up with several countries on one side and many countries on the other. I believe that if it had not been for such a system of alliances, the war wouldn't have been as large or world-wide as it is now. Also, countries also had colonies which helped provide resources and people, which further made turned the wars from regular to "World War"s.
The thing about Japan is that we, the US, is basically their military. As Rex said, after WWII they were demilitarized, and in the treaty it stated (in some way) that the US was to be their military. Granted, they do have a coast guard, but from what I remember in class that was pretty much it.
The issue with Iran isn't as much of a concern as it is with the Koreas, since they're not as developed economically or politically, and even though Iran does have many allies on its side, they're similar to Iran in that they're not as economically or politically developed. That's not to say that the conflict there isn't possible to spark a new WW, but I'm just saying that it's not as possible as it is in Korea.
The Israel/Palestinian peace talks are going relatively well as it is. The US is just worried about Hamas ruinning everything, which could also spark WWIII.
I'm going to throw in the thing about India and Pakistan's claim to Kashmir in the hat as well, since they're both very hostile to each other. I don't know much about who's going to help who if a nuclear war breaks out between them, but it's still very possible that this region could also start a third World War.
As for Europe's involvement, they'll probably get involved if someone drops the bomb on them (literally) for fear that they might join up with the other team, or if they're providing resources for the opposing group. And if one country of Europe comes in, then, thanks to the formation of the European Union, you can guess that most of the other states will join in.
And so, in conclusion, since everyone's pointing nuclear missiles at each other, WWIII is inevitable, and it'll come sooner or later. I'm betting it'll start as several smaller wars, then merge thanks to alliances and whatnot.
