Why was India unable to maintain a unified empire in the first millennium BCE?

India was unable to maintain a unified empire in the first millennium BCE due to its vast geographic diversity, which included varied topographies, climates, and cultures that made centralized control challenging. Additionally, the region was characterized by a multitude of regional kingdoms and tribes, each with distinct identities and governance structures, leading to frequent conflicts and rivalries. The lack of advanced communication and transport systems further hindered the ability to maintain cohesive governance across such a large area. As a result, India experienced a fragmented political landscape rather than a single, unified empire.