The new doctrines arose partly because of the accumulation of historical knowledge, and the growth of the historical sense, which had hardly existed before the nineteenth century. The cyclical movement of history was now intelligible, or appeared to be so; and if it was intelligible, then it was alterable. But the principal, underlying cause was that, as early as the beginning of the twentieth century, human equality had become technically possible. It was still true that men were not equal in their native talents and that functions had to be specialized in ways that favoured some individuals against others; but there was no longer any real need for class distinctions or for large differences of wealth. In earlier ages, class distinctions had been not only inevitable but desirable. Inequality was the price of civilization. With the development of machine production, however, the case was altered. Even if it was still necessary for human beings to do different kinds of work, it was no longer necessary for them to live at different social or economic levels. Therefore, from the point of view of the new groups who were on the point of seizing power, human equality was no longer an ideal to be striven after, but a danger to be averted. In more primitive ages, when a just and peaceful society was in fact not possible, it had been fairly easy to believe it. The idea of an earthly paradise in which men should live together in a state of brotherhood, without laws and without brute labour, had haunted the human imagination for thousands of years. And this vision had had a certain hold even on the groups who actually profited by each historical change. The heirs of the French, English, and American revolutions had partly believed in their own phrases about the rights of man, freedom of speech, equality before the law, and the like, and have even allowed their conduct to be influenced by them to some extent. But by the fourth decade of the twentieth century all the main currents of political thought were authoritarian. The earthly paradise had been discredited at exactly the moment when it became realizable. Every new political theory, by whatever name it called itself, led back to hierarchy and regimentation. And in the general hardening of outlook that set in round about 1930, practices which had been long abandoned, in some cases for hundreds of years—imprisonment without trial, the use of war prisoners as slaves, public executions, torture to extract confessions, the use of hostages, and the deportation of whole populations—not only became common again, but were tolerated and even defended by people who considered themselves enlightened and progressive.