Beidi in the context of "Eurasian steppe"

"Four Barbarians" (Chinese: 四夷; pinyin: sìyí) was a term used by subjects of the Zhou and Han dynasties to refer to the four major people groups living outside the borders of Huaxia. Each was named for a cardinal direction: the Dongyi ("Eastern Barbarians"), Nanman ("Southern Barbarians"), Xirong ("Western Barbarians"), and Beidi ("Northern Barbarians"). Ultimately, the four barbarian groups either emigrated away from the Chinese heartland or were partly assimilated through sinicization into Chinese culture during later dynasties. After this early period, "barbarians" to the north and the west would often be designated as "Hu" (胡).

The Han–Xiongnu Wars or Sino-Xiongnu Wars, were a series of military conflicts fought from 133 BC to 89 AD between the agrarian Chinese Han Empire and the nomadic Xiongnu confederacy, although extended conflicts can be traced back as early as 200 BC and as late as 188 AD.

The Chinese civilization initially clashed with Inner Asian nomadic tribes (then collectively known as Di) that would later become the Xiongnu during the Warring States period, and various northern states built elongated fortifications (which later became the Great Wall) to defend against raids down from the Mongolian Plateau. The unified Qin dynasty, who conquered all other states under Emperor Qin Shi Huang, dispatched General Meng Tian in 215 BC in a successful campaign to expel the Xiongnu from the Ordos region (which was often used as a staging area to threaten Qin's Guanzhong heartland). However, the subsequent civil wars following the Qin dynasty's collapse gave the Xiongnu tribes, who were then unified into a large confederacy under Modu Chanyu, the opportunity to reinvade the Ordos region. After the Han dynasty was established in 202 BC, Emperor Gao tried to fight off Xiongnu invasions but had himself trapped in an ambush during the Battle of Baideng, and a truce was negotiated by bribing Modu's wife, thus ending first Han–Xiongnu War. Decades of de jure peace then followed with the Chinese gifting "harmony via marriage" to appease the Xiongnu, who still routinely raided Chinese borderlands.