In the mid-ninth century, the Central Asian political map experienced tremendous changes. Both external military invasions and internal conflicts brought up challenges to the three great powers of the time, namely the Tang, Tibetan and Uighur empires. Concurrently, the entire region experienced the significant consequences of severe climate change and environmental distress. Near the mid-ninth century, a series of natural disasters hit the eastern part of the Asian continent, verified by both Chinese and Tibetan sources. Nevertheless, the years between 839 and 841 were the deadliest on record, a turning point for the political landscape of Central Asia. First, the Uighur empire collapsed due to attacks by Kyrgyz tribes, and the Uighurs scattered to the Hexi Corridor and Western Regions. Second, the Tibetan empire disintegrated and withdrew from the Hexi Corridor, eventually losing its control over Central Asia. Third, the Tang empire retook the Hexi Corridor and no longer faced the combined threats by the Uighur and Tibetan empires in Central Asia. These changes should be attributed to different responses and coping methods by the three principal powers in Central Asia in handling the natural disasters they faced, based on their different economic systems.

839–841 年：重塑中亞政治版圖之災難歲月

九世紀中期，中亞政治版圖出現巨大變化，而其重塑的原因不僅有各個政權面 臨的外部入侵，也有內部分裂，但其中一個不可忽視的關鍵性因素則是嚴重的 氣候和環境災害。九世紀中前期在亞洲大陸爆發了一系列重大災害，這些災害 在中古時期漢文和藏文文獻中可以得到相互印證。839-841 年顯然是災情最為 嚴重的數年，也是中亞政治版圖變遷的轉折點。首先回鶻被黠戛斯人滅亡，殘 余勢力南下，一部分散落於新疆至河西走廊沿線；其次，吐蕃分裂，逐漸退出 河西走廊，喪失了對中亞地區的控制；再次，唐朝逐漸收復了河西走廊，解除 北方回鶻和西部吐蕃的軍事威脅。由於三大政治勢力基於不同的經濟發展模式，他們應對這些災害的措施也不同，並進而出現不同結果，最後直接影響到三 大政治勢力在中亞的興衰。