The Han–Xiongnu War, also known as the Sino–Xiongnu War, was a series of military battles fought between the Han Empire and the nomadic Xiongnu confederation from 133 BCE to 89 CE.

Starting from Emperor Wu's reign (r. 141–87 BCE), the Han Empire changed from a relatively passive foreign policy to an offensive strategy to deal with the increasing Xiongnu incursions on the northern frontier and also according to general imperial policy to expand the domain. In 133 BCE, the conflict escalated to a full-scale war when the Xiongnu realized that the Han were about to ambush their raiders at Mayi. The Han court decided to deploy several military expeditions towards the regions situated in the Ordos Loop, Hexi Corridor and Gobi Desert in a successful attempt to conquer it and expel the Xiongnu. Hereafter, the war progressed further towards the many smaller states of the Western Regions. The nature of the battles varied through time, with many casualties during the changes of territorial possession and political control over the western states. Regional alliances also tended to shift, sometimes forcibly, when one party gained the upper hand in a certain territory over the other.

The Han Empire eventually prevailed over the northern nomads, and the war allowed the Han Empire's political influence to expand deeply into Central Asia. As the situation deteriorated for the Xiongnu, civil conflicts befell and further weakened the confederation, which eventually split into two groups. The Southern Xiongnu submitted to the Han Empire, but the Northern Xiongnu continued to resist and was eventually evicted westwards by the further expeditions from Han Empire and its vassals, and the rise of Donghu states like Xianbei. Marked by significant events involving the conquests over various smaller states for control and many large-scale battles, the war resulted in the total victory of the Han Empire over the Xiongnu state in 89 CE.