In the 3rd century BC, the Qin state conquered the six other states and established a political system with centralized power. Comprehensive reforms were implemented to standardize the transport, writing, currency and measuring systems and replaced the feudal system with the system of prefectures and counties, laying the groundwork for the governance of a unified dynasty. During the Qin Dynasty (221-206 BC), 36 prefectures were established nationwide, including seven in Henan. Henan became a strategically vital area for supporting and defending the great Qin Empire.