Xiongnu

The Xiongnu was a Steppe Empire (209 BCE-329 CE), consisting of a Nomadic Confederation located in present day Mongolia.
The Xiongnu alternately fought wars with China or received Tribute. Between 220-206 BCE the Qin Dynasty rebuilt and connected Great Wall of China to prevent Xiongnu incursions.

The Xiongnu formed themselves into an Empire in 209 BCE under Modu Chanyu, possibly in response to the unification of China under the Qin Dynasty in 221 BCE.
The frontier between the Xiongnu and China was defined by the Great Wall of China.
The Xiongnu relied on Tribute from China to maintain its confederation.

Between 48-155 CE, the Xiongnu were divided into the Northern Xiongnu and the Southern Xiongnu, and fought each other.
Some historians have put forward a theory that the Northern Xiongnu migrated westward and either merged with or became the Huns.
From 50 CE onwards the Southern Xiongnu became a Tributary State to the Han Dynasty of China, enabling them to keep the Southern Xiongnu in check.

Ban Chao, the senior General of the Han Army, sent 70,000 men against the western region Xiongnu, and ended their raids on the Silk Road, resulting in their subjugation.

Ban Chao then sent his Envoy, Gan Ying, to Daquin (Rome).
Gan Ying reached Hecatompylos and the court of the King of Parthia, Pacorus II (78-110 CE).
But after leaving Hecatompylos, he only reached Charax Spasinou, on the Arabian Gulf.
The Chinese delegation turned back after being advised by the Parthians it would take too long to get to Rome.
They returned to China and handed a complete report, compiled by the Parthians, on the Roman Empire, to the Emperor He of Han (88-105 CE).

Mongolia