Overpopulation can be solved by education. When people are educated, they won't have as many children. The fact that a half of the world does not receive good education is saddening. If all that money we spent on wars went towards developing the world as a whole, we would be far more united and our population situation will be far better than it is now. Also, war does not exactly expel populations rather it creates baby boom periods after millions have been killed and in a few decades the population increases more than it was pre-war. It is definitely not a good way to control population.