The history of Punjab has witnessed the migration and settlement of innumerable races, forming a melting pot of Punjabi civilisation. The first traces of human habitation in India were found in the Punjab region. The Indus Valley Civilization flourished in antiquity before recorded history until their decline around 1900 BCE. The Punjab has had numerous recorded invasions, starting with the Vedic tribes. Punjab was enriched during the height of the Vedic period, but declined in predominance with the rise of the Mahajanapadas. The region formed the frontier of initial empires during antiquity including the Achaemenid, Alexander, Seleucid, and Maurya Empires. After the fall of the Maurya Empire, the region was splintered into multiple kingdoms and republics. Punjab was subsequently conquered by the Kushan Empire, Gupta Empire, and then Harsha Empire. Punjab continued to be settled by nomadic people; including the Huna, Turkic and the Mongols. Circa 1000, the Punjab was ruled by Muslims and was part of the Delhi Sultanate, Mughal Empire, and Durrani Empire. Sikhism originated in Punjab and resulted in the formation of the Sikh Confederacy after the fall of the Mughal Empire and ensuing conflict with the Durrani Empire. This confederacy was united into the Sikh Empire by Maharaja Ranjit Singh.