borders and frontiers: Asia and the Pacific 133 remained out of reach Indeed, the Khitans of Manchuria conquered the far northern regions of China and declared themselves the Liao Dynasty (907–1125) The Song emperors maintained their borders with military force and bribery: They paid their neighbors not to invade them In 1125 the Jurchens from Manchuria drove the Khitans out of China and then seized the northern territories of the Song In 1140 a new border between the Song and the Jurchens, who had established the Jin Dynasty in northern China (1115–1234), was defined south of the Yellow River The Mongols invaded the Jin territory repeatedly, ending the Jin Dynasty in 1234 The Song Dynasty proved to be a more formidable foe, and it took over 40 years of fighting for the Mongols to conquer that part of China Thereafter, the Yuan Dynasty (1279–1368), as the Mongol rulers named their line, pressed southward and southwestward, eliminating the kingdom of Nanzhao The borders of China became confused again when rebels established a new state with its capital at Nanjing In 1368 a rebel leader named Zhu Yuanzhang declared himself the founding emperor of a new dynasty, the Ming By 1382 nearly all of China had been reunited by the Ming rulers Ming armies ranged far north and forced the Mongols of eastern Asia into submission The Ming emperors undertook the complete rebuilding of the Great Wall, constructing the wall as it can be seen today, adding impressive stone fortifications They used the wall to separate farmlands in the south from pasture lands in the north In the northwest the Turks and the Chinese had a hostile standoff that resulted in a remarkably stable border China had difficulty extending its southern borders, but in the 1400s it managed briefly to control most of Indochina and force what is now Sri Lanka, south of India, and much of Sumatra to submit to Chinese authority In the early medieval era there were three kingdoms in Korea: Paekche, Silla, and Koguryo In 936 the name of Koguryo was shortened to Koryo, the origin of the modern word Korea The borders of these three kingdoms were poorly defined in the 600s, with frontiers between the kingdoms sometimes governed by no one In 660 the kingdom of Silla allied with China to conquer Paekche In 668 Silla defeated Koguryo to create Unified Silla After invasions by the Khitans of Manchuria, the rulers of Korea built a wall in 1018 across the Korean Peninsula from the mouth of the Yalu River eastward to Ti-ryo-p’o on the eastern coast This wall served as the northern border of Korea The peoples of India had some natural barriers that helped them develop their own culture apart from the rest of the world To the north lay the Himalayas, a formidable range of mountains that not only discouraged invasions into India but also restrained the efforts of Indian rulers to invade Tibet Most of the rest of India was surrounded by the ocean, providing the land with a rugged coast that would have made invasions by sea very difficult The vulnerable frontier for India was the valley of the Indus River in the northwest, through which Alexander the Great had led his armies in the fourth century b.c.e and through which Muslim armies would attack during the medieval era The notion of what constituted frontiers for the Indians was unique Monarchs would try to fulfill a digvijaya, or campaign in conquest of the four corners of the world The digvijaya involved forcing neighbors to the north, east, south, and west to submit to their authority and pay them tribute This process created a raja-mandala, the “circle of kings.” The mandala represented the cosmos, at the center of which was the mythological Mount Meru, surrounded by four lands, then seas, then lands, and then seas in rings In a raja-mandala the king served as a human representation of Mount Meru, and the lands around his kingdom formed the pattern of the mandala Thus, a medieval Indian map of a kingdom would show it as a mandala with concentric rings spreading out from its center—the king—into the lands of his subjects This way of thinking about frontiers had serious consequences One is that borders and frontiers changed frequently according to who was powerful enough at any given time to force other rulers to submit to his or her authority Thus, much of the history of the borders and frontiers of medieval India involves the expansion and contraction of numerous kingdoms but rarely their unification Moreover, the medieval Indian attitude toward borders and frontiers helps explain why some of India’s mightiest conquerors, such as Rajendra Chola I (fl 1040) of the kingdom of Chola in southeastern India, did not try to retain huge tracts of land Instead, they looted lands hundreds or even thousands of miles away and returned home to the kingdom that served as an earthly representation of the sacred mandala Once a king had completed his digvijaya, the acquisition of wealth from looting may have had more prestige than governing conquered lands Exactly what the borders of Japan were at the outset of the medieval era is a matter that leaves historians bitterly divided Archaeological discoveries suggest that there were two main cultural groups on the islands, the Nihon or Japanese and the Ainu Anthropologists believe the Ainu may be direct descendants of the first modern peoples to inhabit eastern Asia They were fierce warriors who many times defeated Japanese armies in pitched battles At the outset of the medieval era the Japanese were the only rulers of the Japanese archipelago who were officially recognized by the various governments of a divided China They controlled Kyushu and most of Honshu and Shikoku, but the Ainu controlled much of northern