Answer: Emperor Wudi was a Chinese emperor who ruled during the Han dynasty from 141 BC to 87 BC. During his reign, he sought to expand the Han empire and strengthen its military power.
One of the major threats to the Han dynasty during this time was the nomadic Xiongnu people, who were based in the north and posed a constant threat to the northern border of the Han empire. In order to defend against the Xiongnu and expand the territory of the Han empire, Emperor Wudi engaged in a series of military campaigns and also sought to establish alliances with neighboring tribes.
One of Emperor Wudi's most important allies was the Xianbei tribe, who lived to the northeast of the Xiongnu. Emperor Wudi allied with the Xianbei in order to create a buffer zone between the Han empire and the Xiongnu, and he also employed Xianbei soldiers in his campaigns against the Xiongnu.
Another important ally of Emperor Wudi was the Wusun tribe, who lived to the west of the Xiongnu. Emperor Wudi formed an alliance with the Wusun in order to create a two-front war against the Xiongnu, and the Wusun proved to be effective allies in the Han dynasty's campaigns against the Xiongnu.
Overall, Emperor Wudi's alliances with neighboring tribes played a crucial role in his efforts to defend against the Xiongnu and expand the Han empire's territory.