The Indian subcontinent is the birthplace of four of the world's major religions, Hinduism, Buddhism, Jainism, and Sikhism, which makes it, by that measure, the single most productive religious region in human history. These traditions share a common conceptual grammar even as they differ profoundly: nearly all work with karma (the moral law of cause and effect across lives), samsara (the cycle of rebirth), and moksha or nirvana (liberation from that cycle) as the ultimate goal, and dharma as the ordering principle of life. Hinduism, the oldest and largest, is less a single religion than a vast family of traditions, Vedic sacrifice, the philosophy of the Upanishads and Vedanta, the great devotional cults of Vishnu, Shiva, and the Goddess, the epics and Puranas, rooted in the Vedas, the oldest religious literature still in use.
From the same soil, in reaction and dialogue, arose Buddhism and Jainism in the sixth to fifth centuries BCE, and, much later, Sikhism in the fifteenth-century Punjab. The subcontinent also became home to enormous communities of Islam (South Asia holds the largest Muslim population of any region) and ancient communities of Christians, Jews, Zoroastrians (the Parsis), and others. The result is a religious landscape of extraordinary density and continuity, in which the philosophical questions of the self, action, and liberation have been debated without interruption for three thousand years.