There is not going to be another world war in centuries. Why?
Middle orient wars cost the USA billions of dollars to maintain per year. Maybe more. And that's only profitable for them because they get to test, showcase, and sell their weapons.
Can you even imagine how high the price of a world war against a superpower would be? Not to mention the losses, specially if they use nuclear weapons. The consequences would probably be more catastrophic than the ones foreseen in movies and the media. It simply doesn't benefit anybody.
But even if there was one, it would probably end pretty quick once they've wasted all of their nuclear weapons anyways.