The History of India begins with the Indus Valley Civilization, which spread through in the north-western part of the Indian subcontinent, from 3300 BC to 1300 BC. This Bronze Age civilization collapsed at the beginning of the second millennium BC and was followed by the Iron Age Vedic period, which extended over much of the Indo-Gangetic plains and which witnessed the rise of kingdoms known as the Mahajanapadas. In the fifth century, large parts of India were united under Ashoka. He also converted to Buddhism, and it is in his reign that Buddhism spread to other parts of the Asia. In the reign of Mauryas, Hinduism took shape fundamentally.