The true question is not is WW3 will happen, but when WW3 will happen. As soon as North Korea's nukes can reach Washington, D.C., North Korea and China will declare nuclear war upon the U.S. and South Korea. The U.S. will bring its full military might upon China and North Korea to aid South Korea. Naturally, the U.N. and Canada will be there to be peacekeepers by mediating the two sides and protecting civilian targets from becoming collateral damage. At the same time, Syria and Egypt will see that Israel will be vulnerable, as the protective forces of the U.S. in Israel will be moved off to the Korean Peninsula and China, meaning that Syria and Egypt will attack Israel, creating a war on two fronts for the U.S. That is both why and how WW3 will happen.
World War III could happen at anytime. I think people like to think and assume that our country is safe but the fact is we need to be prepared for anything because anything could happen. That is why our troops are constantly pushing themselves and preparing themselves for the worst.
Yes, World War 3 could happen is late or even early future. Nobody can determine whether or not our world will come to and end from total destruction from a war. This war could be caused by inhumane acts or terrorism, or even someone illegally attacking another country(Having no reason to attack). But as I said, this is a possibility and could most likely lead to the end of the world due to the amount of nukes that are created and able to be deployed.
World War III will happen, eventually. North Korea, ISIS, Russia are all possibilities of instigators of WWIII. They have cruel or crazy leaders (ISIS has both), and are looking for war. North Korea is the most likely candidate, since the Interview hackings happened. Get ready for nukes to go off.