There has been a lot of talk about WW3 and the fact that we are in it right now. I disagree. While the world is in a state of constant low grade conflict from several sources, but I do not think we are currently in World War 3. It is possible that the world could enter into another global war, though I doubt the path to that global war lies though the middle east.
In my mind for a war to be called a "World War", it must be truly global in reach and involve all or most of the major power players in the world. The first condition is fairly easy to satisfy in my mind. The second one is a little harder as the major superpowers have to feel that their very existence is at stake to participate in such a huge war. Gone are the days of taking overland and spreading your influence through beating your competitor on the battlefield. For the most part the major powers compete on the economic stage. Though there is a good bit of competition on the world political stage inside of the UN. This is not to say that another world war is not possible, it is just less likely.
So the real question is what possible events could involve Brazil, China, Europe, India, Japan, Russia, and the United States in a battle to the death? I think there are several main paths to world war three, some of which are listed below.
Israel is attacked or attacks Syria, which pulls Iran into the regional conflict. If Iran was somehow able to convince Russia or China to join them, then there is a good chance World War 3 would be on. But what are the chances that Russia or China would actually risk that by supporting Iran, a county that while it does have oil, no one really likes anyways. I suspect that Russia and China would view this as an UN problem, not a problem to actually fight over. Russia has its own oil reserves and China is and has made deals with other middle east countries to buy oil, so it might view the loss of Iran's oil as unfortunate, but nothing to go to war over.
North Korea is attacked or attacks South Korea or Japan. There is a good chance that China would then get directly involved. Unfortunately, the US is already directly involved and has been involved for the past 50 some odd years in that area. If North Korea is let off of it's short chain by China or just gets out of the fence, they could cause some tense situations (like Cuban missile tense). I view this as the shortest and most likely path to WW3. I think of China as the country that we are most likely to end up in a war with in the next 20 years. I also think that if North Korea acts with out China's help or without their permission nothing will come of it. What I am afraid of is China using, North Korea, to draw the US into a larger conflict.
If Hugo Chavez goes "Saddam Hussein" land hungry in south America, you could see another a world war or more than likely see a worldwide rescue like in 1991, in the Gulf War.
Random possibility 5
It is possible, though not probable, that any of the major powers could stage a random attack on one of the others. We have already seen that the US can take over a couple little countries and no one big is willing to fight about it. It would have to be on the scale of China attacking India, Japan, or Russia, for the big boys to get involved. China could probably take over a few smaller countries and no one would really try too hard, though there would be a lot of talk about getting ready for war.
I don't see a global war in the near future, but the seething low level global conflict sure ain't going away. There is also not an easy or clear way of ending the global conflict, with out giving in to the wants of those causing the problems. If I missed something in my global analysis, please chime in with treaties to back up you claims.
Update: I was going to include the fact that Iran and North Korea could team up as one of the potential outcomes, but the fact that Iran was at the missile test for North Korea had not been confirmed. Well know it has.