World War III can and will be avoided. I think the fact that we still have not had a huge war like that again in many years is good proof of that. We are coming to a more peaceful time when the countries are making an effort to get along.
War is something that does seem inevitable because of the greedy and selfish part of human nature that gets played out across nations. However, with some realization of how devastating this next big one would be and with some working together of the larger nations, we might be able to avoid it.
World War III has been proposed to be the arab nations of the middle east aligned with China and possibly Russia. This is not a likely scenario. If such a war was likely, it would last only about 72 hours. The Iraq war was really over in just as much time. The follow on occupation was for security, not victory. Victory was had on the first day.
I believe the human race can avoid World War III but it takes cooperation from all people, which, given our greedy nature, can be difficult. I believe people like taking up sides to quickly or try to pass things off without fully understanding them. I believe it is possible to reach a point where peace is possible, but we have to stop restricting each other.
If world war three were to happen, we all know it would be the end of humanity as we know it, and perhaps humanity as a whole. It would be a frightening apocalypse, and every advancement the human race ever made would basically be washed away. I'd like to think people are too smart for that.