"Khaghan argues that china was the unipolar power in 660. I fail to see how that even qualifies as a unipolar moment let alone being the unipolar power. To qualify as having a unipolar moment a state must have technology and resources that would enable it to gain dominion over the entire world. To be the unipolar power it must do just that.
The whole premise of khaghans argument- that unipolar powers have existed is obviously incorrect. Regional superpowers have existed. States that have achieved a unipolar moment have existed arguably. But a unipolar power? It has not happened. "
No, the definition of a unipolar power simply means a state that have no challenge to its authority. Its irregarldess of global dominance or regional. Tang china is not a world power, or a superpower, except regional, but it is a unipolar power for Tang did however achieve unrivalled hegemony of East Asia, and in relative terms the dynasty probably represents Chinas zenith as a world power. The far western frontier reached the oases of Transoxiana and the mighty Chinese armies established six military protectorates (Du-Du-fu) on the frontiers: An-nan (Hanoi), Bei-ting (Beshbalik in Jungaria or Eastern Turkestan), An-Xi in western Kansu, An-Dong in Liaoning (southern Manchuria), An-bei in the north-west of the Ordos plateau, and of Chang-yü in the north-east of the Ordos plateau, on the Yellow River. These territory are subdivided into even more prefectures, after 647, when the Xue Yang Tuo tribe were defeated, An Bei was set up and aoned into 6 separate du du fu. In 625, Wei Shi of northern manchuria submit to Tang, protectorate was set up their and the tribes were granted Du Du title. In 629, the subjected Kitan was also placed under the An Dong. During the height of Tai Zong's reign, there were 360 Zhou and 1557 protectorates stretching from Manchuria to the Aral Sea, From Siberia into Vietnam.
In Kansu submission was wrung from the Tanguts, opening a narrow corridor to the west, through which the relentless Tang armies poured. In the dusk of Tai-tsungs reign eighty-eight Asiatic peoples recognised Chinese overlordship. The great Tang empire was easily the most populous state in the world, with 52,910,000 people counted in the census of 755. While close to 50 milllion in 660s. Thats not including the Protectorates of the empire. Journal of the Economic and Social History of the Orient, 18 (1975), pp. 271-299, estimates the total population of the Inner Asian Steppe in 1251 as approximately 4,250,000 nomads. This total included approximately 850,000 nomads in Outer Mongolia, approximately 850,000 nomads in Inner Mongolia, a sedentary population of approximately 1,150,000, and approximately 850,000 nomads in Transoxiana, Semirecheiye and parts of Jungaria and the Tarim Basin (but excluding most of Kazakhstan). While Tang territory in Paekche which having a census of 760,000 houshold, roughly equivalent to 4 million individuals, Nan Zhao's appromimately 2.1 million souls, Tang empire with all its protectorate would have reached something roughly equivalent of 65 million souls in a world that has roughly 210 million population, or nearly a third of it. The Islamic empire which is only on the infancy of expansion only has some 20 million souls, 2.5 million sq miles, with a revenue only a third that of Tang and the population of the Byzantine Empire had fallen to only 7,000,000. Tubo was only a growing power, and the sino tibetan competition haven't actually began until the late 660s when Tubo secured its conquest in Qin Hai as a base of operation against Central Asia. Indeed in 660, no power came close to that of Tang in dominance.
Of course as already mentioned, its impossible to compare modern power with ancient power due to the absense of global interaction for the later. But since no power could achieve global predomenence, regional dominance and share of the world;s wealth, subject, military and the like is the key to estimation.
"At lot of things could rip through a Roman scutum if they were to hit at the right angle. What angle of incidence was used in the tests ? Their strength was in their curvature the purpose being to deflect rather than stop. "
The angle was refered to composite bow of the Syrians and Parthians. In the case of crossbow, ripping through at given range is guaranteed.
"There is massive variability in scutum design anyway. Again have they dug up a scutum in China? "
No, but the scutum design is of the Late Republic, which is already the curved rectangular type idnetical to the imperial age.
"Also one must remember that even if it penetrates the scutum it has the lorica segmentata to go through as well. The obvious question is can a bolt from a Han crossbow penetrate a scutum and lorica segmentata? "
It depend on the distance and angle of the hit in this case. The military manual of the Tang mention specifically the distance required to pierce heavy iron armour at whats equivalent of 230 yards, while under 100 yards, its virtually pierless. Dipped in poison with a lead content of 60 percent, a small puncture would be fatal. But one must also remember the obvious; the hand and feet of the legionaire are still unprotected, causing vulnerability, which was demonstrated by the arrow assault of the Parthian archers ar Carhhae.