Final answer:
The Xiongnu Empire was sustained through tribute, plunder, and high taxes.
Step-by-step explanation:
The Xiongnu Empire was sustained through a combination of tribute from China and other pastoralists, plunder from conquest, and to a lesser extent, high taxes from the regions of China and Persia that they ruled over. The Xiongnu were a nomadic people who established a strong military presence, constantly raiding and expanding their territory, which allowed them to accumulate wealth and resources. They also received tribute from China and other neighboring nomadic tribes, further increasing their wealth and power.
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