No one knows. Any World War is pretty far away, and there's no way to tell where it would start. Remember, during the 20's, people had no idea at all that Germany could build itself into a superpower and take on the world. Just because a country is weak now doesn't mean they will stay weak.
On the other hand, strong countries don't have to fight each other. During the Cold War millions of people, my father included, were certainly, absolutely CERTAIN that the USA and the USSR would fight each other. Never happened. So just because China and the US are the main power centers of the world today (or will be soon, China is on the rise), it doesn't mean they HAVE to fight.
So no one can tell.