The history of India begins with the Indus Valley Civilization, which spread and flourished in the north-western part of the Indian subcontinent, from c. 3300 to 1300 BCE. Its Mature Harappan period lasted from 2600-1900 BCE. This Bronze Age civilization collapsed at the beginning of the second millennium BCE and was followed by the Iron Age Vedic period, which extended over much of the Indo-Gangetic plains and which witnessed the rise of major kingdoms known as the Mahajanapadas. In two of these, in the 6th century BCE, Mahavira and Gautama Buddha were born, who propagated their Shramanic philosophies among the masses.
Later, successive empires and kingdoms ruled the region and enriched its culture - from the Achaemenid Persian empire around 543 BCE, to Alexander the Great in 326 BCE. The Indo-Greek Kingdom, founded by Demetrius of Bactria, included Gandhara and Punjab from 184 BCE; it reached its greatest extent under Menander, establishing the Greco-Buddhist period with advances in trade and culture.
The subcontinent was united under the Maurya Empire during the 4th and 3rd centuries BCE. It subsequently became fragmented, with various parts ruled by numerous Middle kingdoms for the next ten centuries. Its northern regions were united once again in the 4th century CE, and remained so for two centuries thereafter, under the Gupta Empire. This period, of Hindu religious and intellectual resurgence, is known among its admirers as the "Golden Age of India." During the same time, and for several centuries afterwards, Southern India, under the rule of the Chalukyas, Cholas, Pallavas and Pandyas, experienced its own golden age, during which Hinduism and Buddhism spread to much of south-east Asia.