This chapter traces the millennium-long migration of the Jat community from their pastoral origins in Sindh to their establishment as a dominant agrarian and political force in the Gangetic Plains. Challenging the rigid dichotomy between nomadic and sedentary societies, it argues that Jat history is characterized by fluidity and adaptation, shaped by the dynamic interplay of ecology, empires, and economies. The analysis begins in early medieval Sindh, where the Jats were first documented as pastoralists, and follows their socioeconomic transition into agro-pastoralists and peasant-soldiers. A key catalyst for their eastward movement was the ecological crisis triggered by the desiccation of the Hakra River, which forced a mass exodus in the thirteenth–fourteenth century. Concurrently, the militarization of the Jats, evidenced in conflicts with the Ghaznavids and their role in Punjab politics, enhanced their capacity for collective action and resistance. The chapter further examines the late medieval period under the Mughals, where state policies selectively managed peasant mobility, often encouraging Jat settlement in the fertile Ganga–Yamuna Doab to boost agrarian revenue. Through this journey, the Jats underwent a significant social transformation, from being outside the traditional caste hierarchy to being classified as Shudras, and eventually forging autonomous polities in the eighteenth century. Their saga underscores the central role of ecological frontiers and migratory corridors in South Asian history, demonstrating how mobility—spatial and social—was a critical strategy for community advancement and resilience in the pre-modern world.