World War III is a touchy yet inevitabel subject. Personally, I think it will have to begin when the United States runs out of oil and the supplying countries refuse to sell any, which will force war. That was actually the reason for Pearl Harbor; the U.S. cut off the oil supply to Japan, only giving them with a few months worth, and Japan had no choice but to declare war.
However, WWIII will be a lot different than everyone would think. It will be nothing like any previous war. It will be done as quickly as possible, and the only way that can be done is with a plethora of nuclear weapons. Nuclear weapons are so advanced today that North Korea could launch one, have it travel all the way around the world, and level an entire American city.In retaliation we will have to do the same, and our allies will help us, which will be the dawn of WWIII.