The geographical area of that history which alone deserves the name has more than once changed. The early home of human society was in Asia. Greece and Italy successively became the theatres of the world's drama, and in modern times the real progress of society has moved within the limits of Western Christendom. So, too, with the material history. At one period the growth of the life of the world is in its literature, at another in its wars, at another in its institutions. Sometimes everything circles round one great man; at other times the key to the interest is found in some complex political idea such as the balance of power, or the realization of national identity.