Why did Emperor Chin have a large spy system?

Emperor Qin Shi Huang, the first emperor of China, established a large spy system to consolidate his power and maintain control over his vast empire. The spy network helped him monitor dissent, gather intelligence about potential threats, and suppress rebellion. By keeping a close watch on officials and the general populace, he aimed to ensure loyalty and prevent unrest, thereby securing his authoritarian rule. This extensive surveillance was part of his broader strategy to unify and strengthen the state.