Xiongnu
Sinologist Edwin Pulleyblank argued that the Xiongnu were part of a Xirong group called Yiqu, who had lived in Shaanbei and had been influenced by China for centuries, before they were driven out by the Qin dynasty. Qin's campaign against the Xiongnu expanded Qin's territory at the expense of the Xiongnu. In 215 BC, Qin Shi Huang sent General Meng Tian to conquer the Xiongnu and drive them from the Ordos Loop, which he did later that year. After the catastrophic defeat at the hands of Meng Tian, the Xiongnu leader Touman was forced to flee far into the Mongolian Plateau. The Qin empire became a threat to the Xiongnu, which ultimately led to the reorganization of the many tribes into a confederacy.In 209 BC, three years before the founding of Han China, the Xiongnu were brought together in a powerful confederation under a new chanyu, Modu Chanyu. This new political unity transformed them into a more formidable state by enabling formation of larger armies and the ability to exercise better strategic coordination. The Xiongnu adopted many of the Chinese agriculture techniques such as slave labor for heavy labor, wore silk like the Chinese, and lived in Chinese-style homes. The reason for creating the confederation remains unclear. Suggestions include the need for a stronger state to deal with the Qin unification of China that resulted in a loss of the Ordos region at the hands of Meng Tian or the political crisis that overtook the Xiongnu in 215 BC when Qin armies evicted them from their pastures on the Yellow River.
Origin of the Huns
Other scholars have put forth evidence from non-European sources to support a link. Writing in third-century China, a Buddhist monk from northern Bactria (modern Afghanistan), named Zhu Fahu (in Chinese) or "Dharmarakṣa" (in Sanskrit), translated the ethnonym "Huṇa" from Sanskrit into Chinese as "Xiongnu". This is the earliest attested usage of the name Huṇa, and Étienne de la Vaissière argues that "the use of the name Huṇa in these texts has a precise political reference to the Xiongnu". A second important piece of textual evidence is the letter of a Sogdian merchant named Nanaivande, written in 313: the letter describes raids by the "Xwn" on cities in Northern China. Contemporary Chinese sources identify these same people as the Xiongnu. De la Vaissière, therefore, concludes that "'Hun/Xwm/Huṇa' were the exact transcriptions of the name that the Chinese [...] had rendered as 'Xiongnu'".
Another important historical document supporting the identification is the "Wei shu". Scholar Friedrich Hirth (1909) believed that a passage in the "Wei Shu" identified the Xiongnu as conquering the Alans and the Crimea, the first conquests of the European Huns. Otto Maenchen-Helfen was able to show that Hirth's identification of the people and land conquered as the Alans and the Crimea was untenable, however: the "Wei Shu" instead referred to a conquest of Sogdia by a group that Maenchen-Helfen identified with the Hephthalites, and much of the text was corrupted by later interpolations from other sources. De la Vaissière, however, notes that a Chinese encyclopedia known as the "Tongdian" preserves parts of the original "Wei Shu", including the passage discussed by Hirth and Maenchen-Helfen: he notes that it describes the conquest of Sogdia by the Xiongnu at around 367, the same time that Persian and Armenian sources describe the Persians fighting the Chionites. Sinor explicitly denied any connection between the Chionites and the Huns, claiming the former to have been Turks, unlike the Huns. However, writing in 2013, Hyun Jin Kim refers to a "general consensus among Historians that the Chionites and the Huns were one and the same". A fifth-century Chinese geographical work, the "Shi-san zhou ji" by Gan Yi, notes that the Alans and Sogdians were under different rulers (the European Huns and the Chionites respectively), suggesting some believed that they had been conquered by the same people.