What measures did Qin Shihuang take to stabilize the north and develop southern Xinjiang?

Building the Great Wall in the north, connecting the Great Wall built by other vassal countries before, setting up Jiuyuan County in the rear of Inner Mongolia and Baotou City in the east, as well as the northern area of Yikezhao League on the south bank of the Yellow River, forming a northern army headed by Meng Tian, with 300,000 troops stationed against the Huns for a long time; In the south, 500,000 Southern Corps headed by Ren Xiao and Zhao Tuo are stationed in Fujian and Peyo of Guangdong and Guangxi: Minzhong County, Nanhai County, Guilin County and Xiang Jun County. In order to transport rations, foot soldiers and immigrants to Lingnan, they dug a canal to connect the Yangtze River water system with the Pearl River water system.