Ancient India had three main geographic regions: the northern plain, Deccan plateau, and coastal plains. Seasonal monsoons brought rain but could cause floods or drought. Early civilizations like the Indus Valley cities of Harappa and Mohenjo-Daro had organized urban planning. Around 1500 BC, Aryan invaders conquered the region and Hinduism developed by blending Aryan and Indian beliefs. Hinduism's caste system rigidly determined one's occupation based on birth. The Mauryan Empire established a strong centralized government under Asoka, who spread Buddhism. The Gupta Empire later ruled as India's golden age of prosperity and trade.