The Turkish Empire (652–745), referred to as Tujue 突厥 in Chinese sources, attracted scholarly attention for being the first traceable nomadic empire in history to be established by the Turks. In 630, the empire came under the control of the Tang Dynasty, but was re-established in 682; for descriptive purposes, modern scholarship calls them the “First” and “Second” empires. Especially in the period of the Second Empire, its ruling members left us with three relevant inscriptions in Old Turkish which, together with Chinese sources, serve as the main focus of research on the empire. However, the information preserved in these sources is too fragmentary to reconstruct the history of that empire in detail. The sources in Old Turkish and Chinese have been available to scholars for over a century; as such, they have been frequently subjected to scholarly analyses. In addition, the number of available sources on this topic has not dramatically increased in recent decades. As a result, the history of the Turkish Empire is a research field in which epoch-making discoveries or significant re-interpretations of its trajectory have been difficult to achieve recently.

Given the above considerations, the book under review is the first monograph on the Second Turkish Empire to be published in many years. Its author, Chen Hao, originally submitted it as his PhD dissertation, signalling a more than welcome intention on the part of the young generation of scholars to continue research on this exciting but challenging topic. The book begins with a short introduction and proceeds to discuss the history of the Second Empire, giving special attention to its military campaigns and diplomatic exchanges with the Tang Dynasty. The author includes, as an appendix, the transliteration, transcription, and English translation of the three famous so-called Orkhon inscriptions. The book also includes a map of the area under discussion, a glossary of Old Turkish words attested in the inscriptions, and a chronology of that empire, which the author refers to as one of his significant new research results.

The author quotes only a few of the previously published studies on this topic and examines their arguments, but he lists a great many secondary sources in the bibliography. For example, there are two different schools of thought about Toñyukuk, who acted as the rulers’ right arm. In Chinese sources, two “rulers’ right arms” appear during Toñyukuk's lifetime: Tunyugu 暾欲谷 and Ashide Yuanzhen 阿史徳元珍. While some scholars consider them to be two different people, others deem them to be the same person. The author agrees with the former theory (pp. 25–7) and takes critical distance from Sergej G. Kljaštornyj, whom he regards as the representative of the latter theory. After Kljaštornyj, however, Mori Masao strengthened the one-person-theory through the comparative reading of Chinese and Old Uyghur sources. Although the author lists Mori's article (p. 26, n. 57), he does not review Mori's arguments. Since the author also takes Chinese sources into consideration to support the two-person theory, it would be relevant to know how his position differs from that of Mori. As this example illustrates, the present author's work could benefit from the detailed examination of all relevant previous studies.

The present study would also benefit from the further use of archaeological sources and research findings. The scarcity of written sources on this topic, mentioned above, could be counterbalanced by considering the available findings of the many archaeological excavations carried out in Mongolia in recent decades. To take just one example, current archaeological analysis indicates that the cultivation of cereals was practised in the Orkhon Valley (e.g. Bemmann et al. “Biomarkers in archaeology – Land use around the Uyghur capital Karabalgasun, Orkhon Valley, Mongolia”, Praehistorische Zeitschrift 89/2, 2014, 337–70). Jan Bemmann and his colleagues date the finding to the period of the Uyghurs, the successors of the Turks. Even if we accept this dating, the fact that the Turks requested grain seeds and farming tools during the Second Turkish Empire to the Tang emperor (p. 53) indicates that the cultivation did not begin suddenly, first under the Uyghur rule. Thus, the author's suggestion that the nomads did not engage in any agricultural activities (e.g. pp. 27–8) should be carefully reconsidered.

The author devotes many pages to discussing in detail marriage negotiations between Turkish and Tang ruling houses, pointing out that no successful marital relationships were established. However, the Tang ruler tried to adopt the daughter of the second Turkish ruler, Kapgan Kagan, who defected from the Turkish Empire to Tang, and marry her to the third ruler, Bilgä Kagan. Mentioning this historical fact would have enriched the author's discussion of this topic. Furthermore, the author upholds the position according to which the status of the ruler bestowing the wife is superior to the status of the ruler being granted a spouse (p. 56). A few years later, however, Uyghur and Tibetan rulers are known to have married Tang princesses, although they held more power than the Tang Dynasty. Even during the Turkish Empire, as the author mentions, there was an agreement for the marriage of the Turkish ruler's daughter and a Chinese prince (pp. 62–3). If one is to accept the author's interpretation, then the candidates for the marriage negotiation should have been replaced once the power balance between the rulers changed. This reviewer finds that further careful examination of the above historical facts is required in order to accept this author's theory.

In his discussion of the writing process of the Old Turkish inscriptions, the author suggests that a part of the text was added only later to the stele (p. 138). The author, however, does not point out any evidential traces on the stone monuments themselves. If some lines had been curved later by other writers, then their script shape, size, line distances and so on would have shown different characteristics. In addition, the writers of the later text probably calculated its length according to the limited remaining free space. Providing a clear solution to the above questions would make the author's discussion of Old Turkish inscriptions worth considering. His discussion indicates, however, that the inscriptions remain privileged objects of research for future studies.