If there is to be a third world war I cannot see this being nuclear. It serves absolutely no purpose other than to wipe out the planet and leave a desolate radiation poisoned wasteland. Apparently the only creatures that can survive a nuclear attack are rats and cockroaches. Once the supply of the few rotting bodies left after the initial blasts and the inevitable radiation sickness has killed the human species, not to mention the vegetation then the rats will turn on each other eventually wiping the rat population out. leaving a planet full of cockroaches and nothing more.
Does one really think the powers that be would actually want to wipe out a planet and leave it inhabitable for many centuries? This does not fulfill any purpose and is a futile exercise in the flexing of muscles. However, there could be a single incident that employs a nuclear missile. It happened in Hiroshima and Nagasaki so its not impossible for it to happen again.
The biggest threat to global security is the very medium I'm using now to post this message. If anyone wants to cause chaos then an all out cyber attack on banks and governmental agencies would render far more damage to society than any nuclear attack could ever do. Why? It's not about killing billions of people, It's about money and power. With a cyber attack there is a long term affect, create chaos to bring about order.