The formation of regions in ancient India was a gradual historical process shaped by geography, ecology, technological developments, agricultural expansion, political organization, trade, and cultural interaction. Between the earliest settlements and c. 300 CE, distinct regions emerged with their own political identities, economic systems, social structures, and cultural traditions. These regions were not fixed territorial units but dynamic spaces that evolved through continuous interaction between human societies and their environments. The Indo-Gangetic plains formed one of the earliest and most influential regions. Initially, the northwestern region was dominated by the Indus Valley Civilization, whose urban centres developed due to fertile river valleys, irrigation, and long-distance trade. After the decline of the Harappan Civilization, the focus gradually shifted eastward into the Ganga-Yamuna Doab and the middle Gangetic plains. The widespread use of iron technology from around 1000 BCE enabled the clearing of dense forests and expansion of agriculture. This led to the growth of permanent settlements, surplus production, and increasing population, laying the foundation for