In past ages, a war, almost by definition, was something that sooner or later came to an end, usually in unmistakable victory or defeat. In the past, also, war was one of the main instruments by which human societies were kept in touch with physical reality. All rulers in all ages have tried to impose a false view of the world upon their followers, but they could not afford to encourage any illusion that tended to impair military efficiency. So long as defeat meant the loss of independence, or some other result generally held to be undesirable, the precautions against defeat had to be serious. Physical facts could not be ignored. In philosophy, or religion, or ethics, or politics, two and two might make five, but when one was designing a gun or an aeroplane they had to make four. Inefficient nations were always conquered sooner or later, and the struggle for efficiency was inimical to illusions. Moreover, to be efficient it was necessary to be able to learn from the past, which meant having a fairly accurate idea of what had happened in the past. Newspapers and history books were, of course, always coloured and biased, but falsification of the kind that is practised today would have been impossible. War was a sure safeguard of sanity, and so far as the ruling classes were concerned it was probably the most important of all safeguards. While wars could be won or lost, no ruling class could be completely irresponsible.