In 100 years from now, the world will be a very different place. Sooner or later, a major military confrontation will take place between the global powers and WW3 will commence, leaving the world in a far worse state than it is now. I hope not, but this is where I see the world headed every time I watch the news.
In my opinion, the chances of another world war is quite low, given the reluctance of various governments to engage in full scale physical confrontations. Human life has grown more valuable over the years and even if the governments decide to start new wars, there is no guarantee that the population is going to support it in terms of manpower and increased taxes.