古代チベット帝國の外交と「三國會盟」の成立

Abstract

The "trilateral" treaty between Tang China, Uighur, and Tibet, which was concluded in 822-823, brought peace to the eastern part of Eurasia. Because of this, the treaty has been recognized as a significant event in the area of concern. Nonetheless, strangely no records of this event exist on the Chinese or Uighur sides, while there are records on the Tibetan side. Despite the fact there has been much scholarship done, the reality of the treaty has not been clarified. Nor has the effect of the treaty on Tibet been addressed. Using numerous historical sources in Tibetan and Chinese, including Dunhuang documents such as Prayers for the foundation of the De ga yu tshal monastery (P.t. 16 + IOL Tib J751), this paper focuses on clarifying the details of the actual process and consequences of the treaty. The conclusions are as follows: ・Previous studies have generally shown that the treaty in 822-823 was concluded between three states, namely Tibet, Tang China, and Uighur. However, Prayers for the foundation of the De ga yu tshal monastery clearly states that Tibet concluded the treaty with "three great states, " namely Tang China, Uighur, and Nanzhao, which indicates that this treaty was actually involved four states. ・The treaty was not of the type where delegations of the four states gathered and determined issues. In fact, leading the international diplomatic efforts, the Tibetan Empire succeeded in simultaneously but secretly concluding individual bilateral treaties with Tang China, Uighur, and Nanzhao. Thus, it seems that Tang China was unaware of Tibet's maneuvers ; consequently, Tang records mentions only the bilateral treaty between Tang China and Tibet. ・The Tibetan Empire proposed the treaties to break Tang China's encirclement of Tibet, which was based on alliances with Uighur and Nanzhao that were forged in the 780 s, and thus proceeded to establish an individual treaty with each state. ・To commemorate the diplomatic success of the series of treaties, the Tibetan Empire carried out numerous Buddhist projects ; however, the excessive cost of the projects resulted in an economic burden that eventually caused the deterioration and collapse of the Tibetan Empire.