Nomadic empire
The Xiongnu were a confederation of nomadic tribes from Central Asia with a ruling class of unknown origin and other subjugated tribes. They lived on the Mongolian Plateau between the 3rd century BC and the 460s AD, their territories including modern day Mongolia, southern Siberia, western Manchuria, and the modern Chinese provinces of Inner Mongolia, Gansu, and Xinjiang. The Xiongnu was the first unified empire of nomadic peoples. Relations between early Chinese dynasties and the Xiongnu were complicated and included military conflict, exchanges of tribute and trade, and marriage treaties. When Emperor Qin Shihuang drove them away from the south of the Yellow River, he built the famous Great Wall to prevent the Xiongnu from coming back.
Modu Chanyu
Modu ruled from 209 BCE to 174 BCE. He was a military leader under his father Touman, and later Chanyu of the Xiongnu, centred in modern-day Mongolia. He secured the throne and established a powerful Xiongnu Empire by successfully unifying the tribes of the Mongolian-Manchurian grassland in response to the crisis of the loss of Xiongnu pasture lands to invading Qin forces commanded by Meng Tian in 215 BCE. While Modu rode and then furthered the wave of militarization and effectively centralized Xiongnu power, the Qin quickly fell into disarray with the death of the first emperor in 210, leaving Modu a free hand to expand his Xiongnu Empire into one of the largest of his time. The eastern border stretched as far as the Liao River, the western borders of the empire reached the Pamir Mountains, whilst the northern border reached Lake Baikal.