Again, within each caste custom rules the lives of the members with much greater force than it can exert in a large and complex society in the absence of the caste system. For each caste has its own tradition and customary code, which is necessarily narrow because of the uniformity of the conditions of life of those who obey it; hence tradition and custom have a narrow and well-defined field of operation; and the narrower the field of its application, the more rigidly will custom control action. The caste system is thus one which permits of great differentiation and specialisation of pursuits, without any weakening of the conservative forces of society. It is for that reason presumably that the social organisation of all early civilisations tended to this form. It was the most easily attained form which combined diversity with stability sufficiently to permit of the formation of a large society or nation; and it was one which made for military efficiency. It formed, therefore, a natural stage of social evolution. In so far as the caste system still survives, it owes its survival to the continuance of the need of the State for military efficiency. And we see how its maintenance is still only rendered possible by its alliance with a State religion and its system of religious sanctions. In Russia, for example, the caste system was thus maintained by the alliance of the military power with the religious system. While we see how in modern Germany the attempt to maintain the caste system and the supremacy of the State over the rights and liberties of individuals is breaking down, as the religious sanctions are losing their hold upon the people. Social democracy, secularism, and the demand for liberty go hand in hand[148]. It is clear, then, that the caste system tends to produce a stable society and to prevent progress; and that, in proportion as it gives way to liberty and equality of all men, both legal and customary, and to the recognition of the rights of individuals as against the State, progress must be favoured.