The main purpose of this article is to try to make clear what in the present condition of the world we can legitimately expect the United Nations to do: a) as regards the maintenance; and b) if aggression should unfortunately recur, as regards the restoration of world peace. These are two very different matters; and it is possible to believe that the first is more important than the second. For the United Nations will certainly have achieved its major purpose if there is no third world war; whereas, if there is, the issue will only to a comparatively minor degree be decided by the United Nations. I know that, stated so bluntly, this thesis may not be accepted by everybody; but the general trend of any argument will be that prevention is better than cure, more particularly if the cure involves the indiscriminate plastering of large areas with atomic bombs and “other weapons of mass destruction”.