The Western Han Dynasty's policy towards the Xiongnu people evolved through four stages. Initially, they used allied marriages, then shifted to military attacks under Emperor Hanwu. After the Mobei War, a policy of amnesty and enlistment was adopted. Following Hanwu's death, a looser policy emphasizing brotherhood was implemented. These changes were influenced by domestic and foreign circumstances, as well as the strength of both the Han Dynasty and the Xiongnu people.