Goguryeo – Sui War The Goguryeo – Sui War were a series of campaigns launched by the Sui Dynasty of China against the Goguryeo between AD 598 and AD 614 . It resulted in the defeat of Sui and contributed to the eventual downfall of the dynasty in AD 618 . Background . The Sui Dynasty united China in AD 589 , defeating the Chen Dynasty and ending the division of the country that spanned almost 300 years . After the unification of China , Sui asserted its position as the overlord of all of Asia , and most countries submitted themselves . However , in Goguryeo , one of the Three Kingdoms of Korea , Pyeongwon and his successor Yeongyang insisted on maintaining an equal relationship with the Sui Dynasty . Wendi of Sui was displeased with the challenge from Goguryeo , which continued small scale raiding into Sui ' s northern border . Wendi sent diplomatic papers in 596 after Sui envoys spotted Goguryeo diplomats in the yurt of the Eastern Turk Khanate , demanding Goguryeo cancel any military alliance with the Turks , stop the annual raiding of Sui border regions , and acknowledge Sui as their overlord . Though Yeongyang appeared to comply with the ultimatum , in the following year , 597 , he launched a joint preemptive invasion with the Malgal against Chinese outposts along the border in present - day Hebei province . Course of the war . First expedition of 598 . Wendi ordered his fifth and youngest son , Yang Liang ( assisted by the co - prime minister Gao Jiong ) , and Admiral Zhou Luohou ( 周羅睺 ) , to conquer Goguryeo with an army and navy totaling 300 , 000 . Yang Liang ' s army faced the early rainy season when it reached Goguryeo . The unseasonably heavy rain made the army ' s progress almost impossible and hampered the transport of provisions . Constant attacks by Goguryeo forces and illness inflicted heavy casualties . Coming to the conclusion that the army could not achieve the objective on its own , Yang decided to combine with Zhou ' s naval fleet and proceed . Zhou ' s navy also came across their own challenges , contending with rough seas , losing many ships despite staying close to the coastline . Whenever they anchored , Goguryeo detachments were present to attack the Sui sailors . The fleet engaged in a battle against a Goguryeo fleet totaling 50 , 000 led by Admiral Gang Isik , presumably on the present Bohai Sea . Already weakened by ambushes and nature ' s onslaught , the Sui fleet suffered a devastating loss . Second expedition of 612 . Preparations . Yangdi , when he won the throne in 604 , built the Grand Canal connecting the north and south of China . The south , economic base of China , and the north , political base of China , were connected by the canal , allowing transportation of troops for the massive military campaign . After the construction of the canal , Yangdi ordered the enlisting of soldiers in 611 . He instructed them to gather in present - day Beijing . The force gathered by year ' s end was one of the greatest in civilization according to the " Book of Sui " . A reported 1 , 133 , 000 troops were mobilized . The army began to depart in early 612 , and due to its size , it took 40 days for all of them to depart . The long line of soldiers stretched for about . Campaign in Manchuria . Yeongyang gave up the buffer zone that he had acquired after the war of 598 , as that the area was not suitable to face such a vast army . The Goguryeo troops retreated behind what is now known as the Liao River . A fortunate event for Goguryeo was that the river melted much sooner than usual . By the time Yangdi arrived , the ice had all melted . Undaunted , Yangdi ordered the construction of three bridges across the river . The bridges however , were too short to reach the opposite bank in another fortunate turn of events for the defenders , and Goguryeo ' s ambush successfully held off the first assault . After the extension of the bridges however , the Sui forces succeeded in crossing the river , and the army surrounded the fortresses of Goguryeo . Yangdi ordered his generals before the campaigns not to make individual decisions regarding the movement of troops , but to report to him to receive instruction . This order hampered Sui strategy throughout the campaign . During the strategically important campaign against Yodong fortress , the general commanding the siege had to send a messenger to the emperor for the approval of the surrender . By the time the messenger returned , Goguryeo ' s troops were again ready to defend the fortress . Exploiting this flaw in the Sui system , Yodong and other citadels of Goguryeo continued to hold on . By June , five months after the start of the campaign , not a single fortress had fallen to Sui . Yangdi felt that a fundamental change in strategy was needed to seize control of northern Korea . Campaign against Pyongyang . The new strategy was to keep the fortresses of Goguryeo in Manchuria at bay , while sending a contingent of army and navy to take Pyongyang , Goguryeo ' s capital . An army contingent , with a strength of 305 , 000 , and a naval fleet of some 200 , 000 were dispatched . Naval assault . The navy reached the bay of the Daedong River before the army . Seeing that the Sui army had not arrived yet , Yeongyang sent a small host to engage the Sui navy in battle . After a short engagement , feigning defeat , Goguryeo troops retreated into the city . The Sui naval commander , Lai Huni , considering this was a chance to add to his merit , led a host of some 100 , 000 to lay assault against Pyeongyang . When the Sui soldiers reached the outer citadel , however , they found the wall empty and the gate open . Upon entering the citadel , they found the valuables and weapons laid out in the open . Being cautious , Lai Huni didn ' t allow looting . While passing through a large Buddhist temple , Goguryeo troops ambushed Sui troops , but it failed and survivors retreated yet again . Lai , considering the ambush in the temple a decisive move of Goguryeo that failed , allowed the looting of the outer citadel . While the looting of the citadel was at its peak , special contingent of Goguryeo troops , consisting of thousands of troops , ambushed the Sui troops . Confused and disoriented , Lai didn ' t offer resistance , but ran to the fleet at the sea , his legion reduced to mere thousands . Disheartened by his failure , Lai changed his plan to wait for army contingent against Pyeongyang and combine to lay siege on the city . Sui army ' s campaign . The army contingent , led by generals Yu Zhongwen and Yuwen Shu , had their own problems . While the supply could be transported safely within China , once it reached Goguryeo territory , there was a danger of ambush by Goguryeo forces . Yangdi solved the problem by instructing each soldiers to carry food for himself , which greatly increased each soldier ' s burden . Many resorted to discarding the food . By the time it had reached Yalu River , the army ' s shortage of provisions was acute . Yeongyang decided to assess the strength of the Sui army by ordering his Commander Field Marshal Eulji Mundeok to fake a surrender and peace negotiation terms with the Sui generals . Generals Wu and Yuwen had their own secret order from Yangdi to seize Yeongyang or Eulji if they should fall into their hands . However , the generals ' advisers , notably the Assistant Director of the Right of the Department of State Affairs , Liu Shilong ( 劉士龍 ) , convinced them it would be unwise to arrest negotiators from the opposing camp . They ultimately let Eulji return to Goguryeo and Yu Zhongwen later regretted his decision , attempting to lure Eulji back . He sent a message that he wished to discuss things further but Eulji , aware of Wu ' s intentions , did not comply . The two generals argued about the next course of action , with Yu Zhongwen arguing strongly that Eulji should be pursued . They did agree that the Goguryeo capital should be captured . Accordingly , the Sui troops began the advancing south towards Pyeongyang . Eulji maneuvered the Goguryeo troops so that they engaged the Sui army seven times a day , each time faking defeat and retreat . The strategy would draw the Sui army deeper south with the perception of victory . The Sui army eventually advanced to about 20 km from Pyeongyang . Yu Zhongwen later recognized that his advancing troops were suffering from exhaustion , and that fortifications of Pyeongyang made for an impossible campaign . Yu reached a dilemma and could not decide on advancing or retreat . Eulji sent him for the occasion a poem : Battle of Salsu River . When Sui army had reached Salsu ( thought to be present - day Chongchon River ) , the water was shallow . Eulji had already cut off the flow of water with a dam . When Sui army had half crossed the river , Eulji opened the dam , drowning many thousands of Sui soldiers . Goguryeo charged the remaining Sui army . The historical text records that Sui soldiers had to run almost 200 kilometers that day to escape death . The Battle of Salsu contributed to the massive overall casualty figure for Sui during the campaign . Emperor Yang crossed the Liao River to attack Goguryeo , initially , with 305 , 000 men . Only 2 , 700 returned . Third expedition of 613 . Yangdi invaded Liaodong again the following year ( 613 ) , but was again obliged to retreat without success . While Yangdi was away , Yang Xuangan , the son of Yangdi ' s prime minister Yang Su , fomented rebellion against Yangdi . Fearing attack from two fronts , Yangdi was forced to retreat and use his army to put down Yang Xuangan ' s rebellion . Fourth expedition of 614 . After crushing the revolt , Yangdi invaded Goguryeo again in 614 . Though he managed to breach Goguryeo ' s first line of defence without capturing the frontier fortress , he could not advance far beyond Liao River due to Goguryeo ' s constant ambushes and obstruction to his supply lines . Yeongyang , seeing a chance to end these exhausting wars , offered peace and returned Yang Xuangan ' s associate Husi Zheng ( 斛斯政 ) , who had fled to Goguryeo after Yang Xuangan ' s rebellion , to Sui . Perceiving the little success in Goguryeo and the increasing internal discontent in China , Yangdi accepted Yeongyang ' s offer of peace and withdrew Sui troops from Goguryeo ' s territory . Aftermath . Yangdi ' s continuous campaigns against Goguryeo resulted in the deaths of millions of people in Sui . The discontent against the regime rose , and after the last campaign , revolts erupted across China . Yangdi moved the capital to the south in Yangzhou , but the revolts were too widespread . The losses that Sui suffered , both in terms of lives and resources and consequently the trust the people had in the Sui state , contributed to the fall of the Sui Dynasty . Peasants , farmers , soldiers , aristocrats , and landlords rose up against the emperor along with many of the dynasty ' s military officers . In fact , Yuwen Shu ' s son , Yuwen Huaji became a powerful Sui general who led a successful coup against Yangdi and personally murdered him .