Kublai Kahns invasion of China
At the time of the death of Genghis Khan in 1227 the Mongol empire had devolved into three groups .The Golden Horde under Berke in southern Russia; the Ill Khan under Hulegu controlling all of the lands up to the west of the Euphrates ; the Chaghadai under Alghu controlling the eastern portion of the steppe to the borders of north western China ,once a Song area who were soon to be displaced by the Jin.
The brother of Genghis, Ogedai, had inherited the empire .There was an internal stuggle for control between relatives leading to ouster of the designated heirs of Ogedai in favor of another branch of the family in which Kublai gained favor. Kaidu, one of the legitimate heirs, was confined to the area between Berke and Alghu. Berke Hulegu and Alghu died leaving Kaidu and Kublai in contention ,Kublai controlling the east ,Kaidu and Baraq controlling Kazakhstan ,most of Uzbekistan ,and also nearly all of Kyrgyzstan.The total scope of this empire stretched
from the River Madar-ya in present day Afghanistan to the Chinese city of Xianyiang on the Han river,the northern limit being lake Balkash on the steppe,the southern one the Tien Shan mountains of mordern day northern Tibet. Upon the death of Baraq ,Kaidu inherited this part of the central Asian empire .
Kublai upon gaining the title of grand Khan proceeded to embark upon the conquest of China taking the northern Jin empire and then pausing in order to contemplate the invasion of the south. The south was a much more daunting proposition as it was not suited to the Mongol style of warfare .The Mongol fought from horse back using quick raids and lightening retreats in order to wear down of the enemies means of sustenance :his farms , small towns and villages.This was applicable to the plains of northern China only .The southern part of the country comprised of hills, valleys, and broken farmland interspersed with cities, their populations some times numbering in the millions .At this time the Empire of the Song numbered some nine millions ,Kublai only able to muster less than a million.
Kublai did eventually conquer the south ,but not without a great deal of tribulation. First there was the rebellion of Ariq ,who had been left in command of the north and stationed in the Mongol capital of Karakorum;then there was the first Mongol defeat at the city of Xianyang situated on the Han river controlling access to the Yangtze river ,the gateway to Hangzhou (Canton).This city was linked to the city of Fencheng situated on the oppostite bank connected by a pontoon bridge spanning the river Han. The walls of Xianyang were some six to seven meters thick encompassing an area of five kilometers wide,the main entrances leading out to a waterway impossible to ford in the summer ,in the winter an impassable swamp and series of ponds and mud flats.
Key to the Mongol success was the construction of a new type of trebuchet which used explosive shells. Explosive shells had been in use in China for centuries but what was new was the counterweight type of trebuchet as opposed to the torsion type giving greated range and accuracy as it was easier to judge the weight of the counter weight than the torsion generated by repeated windings.The design was taken from those used by Hulegu to batter down the walls of Baghdad,thus bringing a five year siege to an end .In 1268 Fencheng capitulated,the Mongols putting the entire population to the sword ,piling the bodies in such away as to be visible over the tops of the walls by those at Xianyang.
Bayan ,the Mongol commander,then sent half of his force up river to wade to the south bank in order to build a bridge across to take the Yang lo fortress .Three thousand Song boats came up the Han river and were repulsed;fifty boats destroyed with 2,000 dead. Xianyangs commander then surrendered to the Mongol commander ,the entire force including the surrendering commander sailing down the Yangtze, the forts along the way falling as this commander ,now allied with the Mongols, had also commanded many of the down river garrisons.
As the Mongols swept south the Song ,in ever greater numbers, committed mass suicide , loath to kowtow to barbarians. Kublai was now in possession of the greatest empire the world had ever known; however this was the Yuan's(as they were later to bemome known) greatest southern advance. Annam(north Vietnam)and Campa(South Vietnam )were invaded but using guerilla tactics prevailed, as too did Burma. Japan was invaded twice and in both instances prevailed. Mythology puts the Japanese victory down to the typhoon which blew up on the second attempt and a storm on the first.Others claim that the long supply line ,combined with the Japanese defensive wall and the temporary suspension of clan conflict was the reason for the Mongol defeat.