In one of these epochs of historical movement, at the opening of the eighth century, there arose the kingdom of Puhai, the capital of which was the present city of Kirin. Its northern boundaries first touched the Sungari, and later the Amur, shifting to the Sungari again. Its southern border was at first the Tumen River, and later the modern province of Ham-kiung was included in it. Lines drawn southwardly through Lake Hanka on the east, and Mukden on the west, would enclose its longitude. Its life lasted from about 700 to 925 A.D. This kingdom was continually on bad terms with China, and the Tang emperors for nearly a century attempted to crush it into vassalage. Puhai made brave resistance, being aided not only by the large numbers of Koraians, who had fled when beaten by the Chinese across the Tumen River, but also by the Japanese, whose supremacy they acknowledged by payment of tribute. With the latter their relations were always of a peaceful and pleasant nature, and the correspondence and other documents of the visiting embassies to the mikado’s court are still preserved in Japan. Yet though Puhai was able to resist China and hold part of the old territory of Korai, it fell before the persistent attacks of the Kitan tribes, whose empire, lasting from 907 to 1125 A.D., stretched from west of Lake Baikal to the Pacific Ocean. In the early part of the tenth century this Puhai kingdom, whose age was scarcely two centuries, melted away again into tribes and villages, each with its chief. The country being without political unity returned to unhistorical obscurity, as part of the Kitan empire. Without crossing the Tumen, to enter China by way of Corea, the Kitans marched at once around the Ever-White Mountains and down the Liao Tung valley into China. The breaking up of Puhai was not without its influence on the Corean peninsula. As early as the ninth century thousands of refugees, driven before the Kitans or dissatisfied with nomad life on the plains, recrossed the Tumen and a great movement of emigration set into Northern Corea, which again became populous, cultivated, and rich. With increasing prosperity better government was desired. The worthlessness of the rulers and the prospect of a successful revolution tempted the ambition of a Buddhist monk named Kung-wo who, in 912 A.D., left his monastery and raised the flag of rebellion. He set forth to establish another political fabric of mushroom duration, which was destined to make way for a more permanent kingdom, and, in the end, united Corea.