Though it is not so many years since the Great War, and the feeling of ' never again ' which followed it. the fear of war is by no means a matter of the past. Everywhere it is being discussed, and everyone has his theory of the principal cause. Some find it in the imperfections of political systems ; others in the economic system, the private manufacture of arms, the pressure of expanding population, or simply human nature. In this series some of the leading thinkers on this problem will give their views and as far as possible all points of view will be represented.