On his deathbed Chingiz Kha’Khan had laid out the vast lines of action that his successors were to follow. One these include the conquest of Myanmar. The two small Chinese states in Yunnan, namely Lai Liu and Yung Chang had been made vassals of Myanmar by tribhuvanAditya and remained so till the reign of Narasimhapati. Kublai Kha’Khan sent his greatest generals, Baghatur Uriangkhadai, son of Subedai, of one of the greatest warriors of Chingiz, to annex these territories. Uriangkhadai was assisted by an advance raiding party under the Mongol warrior Soegetue Noyan, and an auxiliary force led two Chechnyan generals Ali Haiya and Nassireddin. Soegetue’s advance force seized Lai Liu and Yung Chang and beheaded its rulers. Then he sent a messenger to Narasimhapati to humbly surrender to the Mongols and hand over his kingdom to Kublai Kha’Khan. Proud over his strength the Burman king refused and declared his intentions to seize back the provinces of Yunnan. Then Soegetue made a move with Nasser towards Myanmar from Yunnan in the North West. This drew the Burman army in that direction, as Uriangkhadai marched in from the North and seized the relatively undefended Northern Mynamar through a swift campaign and moved in to occupy Bhamo. The conquest of Bhamo opened the path to the Iravati (Ayerayawaddy) valley and gave them a straight route to arimardanapura (Pagan). Uriang then secured a forest in the vicinity of Bhamo and planned his attack on the Burman interior. Shaken by move Narasimhapati sent a force of 60,000 men to take on Uriang. Of this around 10000 made the elite Burman cavalry and the frontline was made of a large elephant force with archers borne on howdas. Uriang led a charge but his horses seeing the elephants fled in terror and for some minutes the Mongols failed to check the beasts under them. This made the Burmans bolder and they advanced forward boldly. However, Uriang noticed that the elephants lacked armor and ordered his men to dismount and shower arrows on the elephants. The Mongol archers, with strong armor and being able to hit targets with their iron-tipped arrows from a much greater distance than the Burmans who only shot bone arrows, held the upper hand in such a confrontation. The elephants wounded all over by the arrows fled backwards into the forest and their howdas broke and sent the archers crashing down. With the elephants out of the way the Mongols remounted and covered the Burmans with swarms of arrows. When they were weakened, Uriang led a direct charge with the cavalry to cut the poorly armored Burmans to pieces with their swords and axes. The Mongols captured 200 elephants in the campaign and incorporated them as draught beasts. Having destroyed the Burman army, Uriang marched along to the Iravati valley to conquer the entire northern Burma but did not move further due to their horses not standing the oppressive heat.
In winter of 1283 Kublai Kha’Khan sent his general Siankur Noyan to slay Narasimhapati and put and end to the Burman kingdom once and for all. A fierce Mongol army with spread through the Iravati valley to destroy all the major Burman cities and grind down the Burma economy. A division of engineers of the Mongol army appeared near the city of Katha on the Iravati and set up huge engines hurl enormous stone missiles on it. In November of that year the assault began with Mongols hurling a hail of ballistas crushing everything in the city that they fell on. The Burmans having never encountered anything of this kind gave up all hopes of defense and fled in terror. Narasihapati sent a strong Burman fleet on the Iravati to relieve his northern defense from the Mongols. However, Sianchur sent his cavalry and infantry on either side of Iravati river to hurl storms of stone ballistas and fireworks on the Burman fleet. Several of their barges were sunk and the river was said to be reddened by their blood. Narasimhapati fearing a total route fled his capital. However, the Mongols paused their campaign against Myanmar to move east and devastate the mahArAjas of Thailand and Indo-China who were bravely defending their independence. In this context the valiant struggle of mahArAja indravarman the 4th of Cambodia, with his guerrilla troops, was particularly noteworthy.
Once this flank clearing operation was done with the Mongols decided to trap Myanmar in a pincer grip, in 1287. One Mongol army under Sianchur advanced from the north, which had already been conquered, while Uriangkhadai marched from the east to intersect at Pagan. First the Mongol raiding parties destroyed major cities and blockaded the ports of Myanmar to cause an economic paralysis. This resulted in the total breakdown of the central authority of the aniruddhan dynasty and local tribal rebellions of the Shan tribes broke out. The chaos prevented any concerted action by the Burman army which splintered up rapidly. At this point the two Mongol generals marched straight on arimardanapura (Pagan) to deliver the coup de grace, even as Narasimhapati was assassinated by agents of the Mongols. The ramshackle Burman army led by the general Ramya was overwhelmed by the Mongol armies and butchered completely. He made his final stand in Pagan, which was besieged by the Mongol generals and assaulted with trebuchets which hurled rocks over a ton on the fortifications. When the cities defenses were broken the Mongol army stormed it and massacred the population and burnt it down. With that the conquest of Myanmar had been achieved and it became a vassal of the Mongols. Kublai Kha’khan was pleased with his generals and rewarded them richly for the great task. Puppet agents from the Shan tribe were placed for administrative purposes in the captured territory. An important consequence of this event was that Burma moved out of the Indian sphere of influence and was appended to the Mongol (to be inherited by the Chinese) sphere. This was especially so because it also corresponded to a low-point in India’s history: its fall under Moslem occupation was underway. The other important issue with the Mongol invasion of Burma was the devastation of its economy, that never allowed its unity to recover completely to the pre-Mongol period.