The Han-Xiongnu War, a series of pivotal conflicts between the two most powerful empires in early Iron Age Eastern Eurasia, was investigated through an integrated multidisciplinary approach encompassing genetics, geology, anthropology, and archaeology. This study focuses on the analysis of a mass grave at the Bayanbulag site (BBS) in Mongolia, initially identified as a Xiongnu fortress. Our primary objective was to identify the individuals buried in the grave, providing deeper insights into the tactics and interactions of the Han-Xiongnu War. Through meticulous archaeological and anthropological investigation, we confirmed the site's war-related nature, evidenced by the fortress's architecture, excavated weapons, and trauma on the remains. Genomic analysis of the remains revealed a genetic affinity with present-day Han and ancient Northern Chinese populations. Strontium isotope analysis offered the critical evidence of the individuals' military affiliation, indicating their origin from regions beyond the Mongolian Plateau, specifically North China and the Central Plains, confirming their identity as Han soldiers. This result is further supported by carbon and nitrogen stable isotope analysis, which revealed dietary characteristic of agricultural populations from North China. By integrating data from various disciplines in a mutually supportive manner, our study presents a comprehensive account of the Han-Xiongnu War, offering new insights into the military organization and strategic engagements of the period. This interdisciplinary approach significantly enriches the historical narrative and contributes to the existing body of knowledge on early Eastern Eurasian conflicts.