Over the centuries China has faced two main threats: internal rebellion and the threat of invasion from across the steppe. (Borders as we now know them never existed in northern China until the founding of the country of Mongolia in the 19th century after the fall of the Qing). The first threat was met by mounting military expeditions into the steppe in order to disrupt the supply lines of the invaders. Pastoral nomads need a secure base of supply from which to obtain such things as iron weapons and cavalry equipment, as these could be manufactured on the steppe. In addition to this trade goods needed to be obtained from civilized societies in order to hold them over the winter months.
Commodities were obtained from the fertile areas within land basins, these basins sustained year round settlement by capturing rain water allowing for the growing of crops, this in turn allowed wandering horse borne societies to exist. What they could not obtain though their own efforts they obtained by trading with the civilized societies to the south through barter or plunder. Three areas of cultivation were available on the steppe: the Tarim basin in China's northwest frontier region; the Dzungaria basin to the north across a mountain range; the Orkhon river district one thousand miles to the east. Control of these areas equaled the control of the Steppe.
Straddling the nomadic trade routes remains of walls have been found on the western steppe built prior to the first unification of China. As these were well to the north of any Chinese settlement of the day it is theorized that they were used as a base from which to raid camel caravans coming from the west. During the reign of the Qin dynasty a series of wall's were built to the north west of the Ordos desert extending to the Jade gate of Yumen located near present day Lop Nor (now the Chinese space centre). This, the first of the long walls built to protect Qin traders going west and to control barbarians issuing from the north.
Barbarian invasions into China during ancient and in medieval times was through the Ordos desert, an area of steppe land within the great northerly loop of the Yellow River. This desert was not able to support civilized society but was (and still is) an ideal spot for nomadic tribes, its lush grass lands suitable for the grazing of the small tough horses of the barbarians .With the first unification of China in 221 BCE by Qin shihuang there began the eviction of the barbarian tribes .General Meng Tien cleared them from these areas by building a wall across the top of the Yellow River loop as he did so.The subsequent Han dynasty lost control of the Ordos and so was forced into a drawn out pacification program whee tribute would be paid in lieu of peace.
The military base for these Han forces was the city of Hsia -an, just north of the Yellow rivers east west course, close to the beginning of its northerly course, giving access through the passes following the northerly course of the river.
The Mongol empire
In the year of 1251 the Mongol empire extended from the North West shore of the Pacific Ocean to the Volga River in the east ,in the north reaching to the lower course of the Danube at Lake Baikal and south to Annam ,(North Vietnam). This bought about a traffic in culture resulting in an influx of Buddhism into China causing the Mongols to lose their reluctance to invade the country,(as they were unwilling to rule through Confucian trained intermediaries).Genghis Khan had begun the process with his attack upon Beijing but had failed to carry on the process .The Mongol Empire was in process of expanding to the east as far as Baghdad under Hulegu, and to the south west and south east (Tibet and the Jin Empire).The Great Khan had impressed upon his brother Kublai that in order to conquer the domain of the Song he would first have to have a western base from which to make inroads .The conquest of Tibet and Yunnan and the latter′s conversion to Islam by the settlement of Arabs and others from the Mongol mid eastern territories within it satisfied these requirements.
Contrary to popular opinion Genghis Khan did not incorporate Tibet into the Mongol empire. The credit for this must go to Kublai Khan who realized that in order to administer the Chinese portion of the Empire he could use the vehicle of Buddhism and so enlisted the Lama Phags-pa as his guru .He convrted to Buddhusm and then made several minor expeditions into parts of Tibet but never did fully pacify the country, or make it accept Mongol rule.
The Mongols, unlike the Huns and the Hsiang-nu ,were politically united and so managed to conquer the north western portionof China ,at the time the Jin Empire. Kublai now built his capital city north of Beijing in order to be in touch with the Mongol capital of Karakorum naming in Xaundu. This has been made famous by the poet Coleridge .However the real capital bore little resemblance to that of the latter day poet Coleridge.
The stage had now set the stage for the conquest the northern portion of the Song Empire and finally, after years of effort, the taking of the city of Xianjiang on the river Wei,gateway to the southern course of the Yangtze. With this city taken Kublai finally managed to subdue the entire south reaching the city of Zhengzhou(Canton),the proud Song capital ,who′s dynasty spanned 300 years.Rather than to submit to the barbarian invaders thousands of Chinese ong committed mass suicide.
However the Mongols too suffered defeat, one when two naval expeditions to Japan were turned back ,strangely enough the weather having a major role in both instances(the divine wind).In addition the Mongols also suffered defeat in Iran, in Iraq, in Java,in Vietnam and in Burma.
In 1271 Kublai Kahn, ever the diplomat , adopted the Chinese name of Yuan, derived from the I Ching,a mystical religious book having grounding in the original Chinese state. The Chinese however remained hostile to not only the Muslim religion, but also to their denigration of status to that of third class citizens ,or even lower in some cases. The Mongols had set up a class structure wher the top echelon were those of the ruling tribe, the next those of the Mongol race ,the next rung the tribes from the steppe ,followed by the northern Chinese ,the lowest the Chinese from the south. In between were a variety of sub states , one for instance were Confucian scholars ,one rung below prostitutes, one rung higher than the lowest : the beggars.