 Complete the following phrase:  The commandery was created during King Wuling of Zhaos reign after a successful campaign against the Linhu 林胡 and Loufan 樓煩 peoples. After the establishment of Han dynasty, the commandery became the frontier between Han and the Xiongnu. In early Han dynasty, the region saw frequent Xiongnu raids. However, from Emperor Wus reign onwards, it became an important base of military operations in the 