From WIKI
**World War III **(WWIII), also known as the Third World War, is a hypothetical worldwide military conflict subsequent to World Wars I and II. Because of the development and use of nuclear weapons near the end of World War II and their subsequent acquisition and deployment by many countries, it is feared that a Third World War could cause the end of human civilization and most or all human life on Earth. A common hypothesis is that a small number of people could survive such an Armageddon, possibly in deep underground blast shelters or away from Earth, such as on the Moon or Mars or in space vehicles. Another major concern is that biological warfare could cause a very large number of casualties, either intentionally or inadvertently by an accidental release of a biological agent, the unexpected mutation of an agent, or its adaptation to other species after use.
USA+NATO or Russia+China
Why do you think it would be nuclear? I actually believe the mutually assured destruction principle is a pretty good guidestone at present to see where the likelihood of a real full out nuclear war erupting.
More likely, I believe we are entering a new era of warfare where the surface area of the battlefield covers an ever expanding multi-dimensional space wherein the new battlespace will revolve around information gathering, behavioral analytics and overall just "mastering the human domain". If there is a war I believe it will be coordinated between countries with the intention of diverting the energy of an increasingly angry population to a common enemy who can be blamed for the problems they experience.
I honestly think the head of state in most countries actually see much more similarities between each other than they do themselves and the proletariat