World War III isn't going to happen because it already did. It's referred to as the Cold War.
World War IV is not going to happen. With the advancements of nuclear weapons, not one country from either side wants to start it. Why? Because if just one bomb is dropped - we're finished. Life destroyed.
It's likely to escalate into a full-blown war which would result in the deaths of millions, perhaps a near billion people across the planet. That's the beginning.
We just wouldn't survive, especially with Putin and Trump as the two most powerful leaders. The United States and Russia have the most weapons and two of the biggest armies.