Many features of Hinduism, its steady though slow conquest of India, its extraordinary vitality and tenacity in resisting the attacks of Mohammedanism, and its small power of expansion beyond the seas are explained by the fact that it is a mode of life as much as a faith. To be a Hindu it is not sufficient to hold the doctrine of the Upanishads or any other scriptures: it is necessary to be a member of a Hindu caste and observe its regulations. It is not quite correct to say that one must be born a Hindu, since Hinduism has grown by gradually hinduizing the wilder tribes of India and the process still continues. But a convert cannot enter the fold by any simple ceremony like baptism. The community to which he belongs must adopt Hindu usages and then it will be recognized as a caste, at first of very low standing but in a few generations it may rise in the general esteem. A Hindu is bound to his religion by almost the same ties that bind him to his family. Hence the strength of Hinduism in India. But such ties are hard to knit and Hinduism has no chance of spreading abroad unless there is a large colony of Hindus surrounded by an appreciative and imitative population[22]. In the contest between Hinduism and Buddhism the former owed the victory which it obtained in India, though not in other lands, to this assimilative social influence. The struggle continued from the fourth to the ninth century, after which Buddhism was clearly defeated and survived only in special localities. Its final disappearance was due to the destruction of its remaining monasteries by Moslem invaders but this blow was fatal only because Buddhism was concentrated in its monkhood. Innumerable Hindu temples were destroyed, yet Hinduism was at no time in danger of extinction.