Emperor Qin Shi Huang, the first emperor of a unified China, ordered the dismantling of the walls of the various warring states for several reasons. One primary motive was to consolidate his power and integrate the various regions into a single, cohesive empire. By tearing down these walls, he aimed to prevent the former states from fortifying their defenses against him, ensuring that they could not rebel or defend themselves against his rule.
Additionally, while the materials from the dismantled walls could have been used to construct the Great Wall of China, it is not as clear that this was a primary motivation. The Great Wall was built not only to defend against invasions, particularly from nomadic groups to the north, but also to symbolize the strength and unity of the newly established Qin dynasty. By integrating the landscape and dismantling the barriers that existed between the various states, Qin Shi Huang aimed to strengthen his control over the newly unified territory.
In summary, while the destruction of the walls served multiple purposes, the key motivations were to centralize power, prevent rebellion, and enhance control over the newly unified empire.