Transition from Sui to Tang The transition from Sui to Tang ( 隋末唐初 ) refers to a period in which the Chinese dynasty Sui Dynasty disintegrated into a number of short - lived states , some ruled by former Sui officials and generals and some by agrarian rebel leaders , and then those states were consolidated into Tang Dynasty , founded by the former Sui general Emperor Gaozu of Tang ( Li Yuan ) . The period roughly started from 613 , when Emperor Yang of Sui launched his first of three campaigns against Goguryeo , leading to a number of desertions from the army and the start of agrarian rebellions against Sui , to 628 , when Emperor Gaozu ' s son Emperor Taizong of Tang ( Li Shimin ) destroyed the Liang state ruled by the agrarian rebel ruler Liang Shidu and reunified China . Sui campaigns against Goguryeo and the start of rebellions . As of 611 , Sui Dynasty had just enjoyed more than two decades of peace and prosperity , as China had been united under it since it destroyed Chen Dynasty in 589 , and aside from border conflicts with Eastern Tujue ( which had since become a vassal state under its Qimin Khan Ashina Rangan ) and Goguryeo , and one brief internal conflict between Emperor Yang of Sui , who became emperor in 604 , and his brother Yang Liang the Prince of Han , the realm had not seen war . When Goguryeo ' s king Gao Yuan ( King Yeong - yang ) refused to pay homage to Emperor Yang in 610 , Emperor Yang decided to plan a campaign to conquer it , and both he and the people believed that the conquest would be easy . The logistics of staging the attack on Goguryeo , however , took much human and other tolls , as the building of a fleet and , particularly more so , the shipping of food and other supplies to the base of operations , Zhuo Commandery ( 涿郡 , roughly modern Beijing ) , caused major disruptions in the farming cycle and major deaths in those conscripted to ship the supplies to Zhuo Commandery . In response , in 611 , in northern China , those who were unwilling to be conscripted began to rise as agrarian rebels , led by leaders such as Wang Bo ( 王薄 ) and Liu Badao ( 劉霸道 ) , and while Emperor Yang initially did not consider these rebels serious threats , the local governmental militias were unable to quell them . Despite this , Emperor Yang launched his first campaign against Goguryeo in 612 , crossing the Liao River into Goguryeo territory in spring 612 . Emperor Yang personally led part of the army to put the important city Liaodong ( 遼東 , in modern Liaoyang , Liaoning ) under siege , while he sent the generals Yuwen Shu and Yu Zhongwen ( 于仲文 ) to lead the rest of the army deep into Goguryeo territory , heading toward the Goguryeo capital Pyongyang , joined by the fleet commanded by the general Lai Hu ' er ( 來護兒 ) . Emperor Yang , however , was never able to capture Liaodong , while Yuwen and Yu , advancing nearly to Pyongyang , were crushed by the Goguryeo general Eulji Mundeok at the Battle of Salsu and forced to withdraw with heavy losses . By fall 612 , Emperor Yang was forced to terminate the campaign and withdraw as well , with only minor territorial gains . About 300 , 000 men had been lost in the campaign . Not deterred , Emperor Yang launched a second campaign against Goguryeo in 613 , even though the agrarian rebellions were becoming more numerous and serious . He again headed for Liaodong himself and put it under siege , while sending Yuwen and Yang Yichen toward Pyongyang . While he was sieging Liaodong , however , the general Yang Xuangan , in charge of logistics near the Sui eastern capital Luoyang , rose in rebellion , attacking Luoyang . When Emperor Yang heard the news , he withdrew his forces and sent Yuwen and Qutu Tong ( 屈突通 ) back to Luoyang ahead of himself , and Yuwen and Qutu joined with Fan Zigai ( 樊子蓋 ) and Wei Wensheng ( 衛文昇 ) , the commanders of forces that Emperor Yang had left at Luoyang and Chang ' an respectively , to defeat Yang Xuangan . Emperor Yang carried out heavy - handed reprisals against actual or perceived adherents of Yang Xuangan , but such actions did not deter further rebellions . Despite this , Emperor Yang launched a third campaign against Goguryeo in 614 . As Lai reached the Yalu River , however , Goguryeo submitted , sending Yang Xuangan ' s confederate Husi Zheng ( 斛斯政 ) , who had fled to Goguryeo , back to Sui as a sign of submission . Emperor Yang terminated the campaign , but when he again summoned Gao Yuan to pay homage to him , Gao Yuan ignored his summons . Emperor Yang began to plan a fourth campaign , which , however , he was never able to launch . Meanwhile , in fall 615 , when Emperor Yang was visiting the northern city of Yanmen ( 雁門 , in modern Xinzhou , Shanxi ) , Qimin Khan ' s son and successor Shibi Khan Ashina Duojishi , who had been displeased by Emperor Yang ' s attempt to keep Eastern Tujue submissive by dividing them , launched a surprise attack on Yanmen , putting it under siege . Sui forces , largely still loyal to Emperor Yang , rushed to Yanmen to try to lift the siege , and Emperor Yang himself promised great rewards for those who came to his aid . After the siege was soon lifted , however , he reneged on the promises , causing resentment among the military . Disintegration of the Sui state . Despite ( or perhaps because of ) increasing agrarian rebel activities in northern China , however , Emperor Yang did not return to Chang ' an or stay at Luoyang , but went to Jiangdu ( 江都 , in modern Yangzhou , Jiangsu ) in fall 616 . With his departure from Luoyang , the rebels near Luoyang coalesced under the leadership of Yang Xuangan ' s former strategist Li Mi , who was proclaimed the Duke of Wei and considered the presumptive eventual emperor by most rebel leaders throughout northern China . Li , however , was not able to capture Luoyang and never claimed imperial title . Meanwhile , Yang Yichen made an attempt to destroy the rebels north of the Yellow River , but while he enjoyed some successes , Emperor Yang and his prime minister Yu Shiji , fearing Yang Yichen ' s military strengths , recalled him under guise of a promotion , allowing the rebel activities north of the Yellow River to reinvigorate themselves and become difficult to control , under the leadership of Dou Jiande . By 617 , a number of other major rebel leaders also began to control significant portions of territory . These include : Several of these rebel leaders — including Li Yuan , Liu Wuzhou , Liang Shidu , Dou Jiande , and Gao Kaidao — formally submitted to Ashina Duojishi and received Eastern Tujue military aid , with Ashina Duojishi ' s strategy apparently to keep China divided . In winter 617 , Li Yuan captured Chang ' an , declaring Yang You emperor ( as Emperor Gong ) , while honoring Emperor Yang as " Taishang Huang " ( retired emperor ) ; these declarations were not recognized by most of Sui territory , which still recognized Emperor Yang as emperor . Li himself became regent with the title of Prince of Tang . Death of Emperor Yang , founding of Tang , and end of Sui . Meanwhile , Emperor Yang , while realizing that the empire was in turmoil , felt secure under the protection of the elite Xiaoguo Army ( 驍果 ) at Jiangdu , and while he sent his general Wang Shichong to Luoyang to try to defend Luoyang against Li Mi ' s attacks , appeared to do little to quell the rebellions otherwise . Not wanting to return to northern China , he considered officially moving the capital to Danyang ( 丹楊 , in modern Nanjing , Jiangsu ) , south of the Yangtze River ) . Meanwhile , the Xiaoguo Army soldiers , who were predominantly northerners and missed their homes , began to desert , and this met with heavy - handed punishment from Emperor Yang . In fear , the remaining Xiaoguo Army officers formed a plot , supporting the general Yuwen Huaji the Duke of Xu ( Yuwen Shu ' s son ) as their leader . In spring 618 , they carried out a coup and killed Emperor Yang . Yuwen declared Emperor Yang ' s nephew Yang Hao the Prince of Qin emperor , but keeping power himself as regent . He abandoned Jiangdu and headed back north , commanding the Xiaoguo Army . Soon , news of Emperor Yang ' s death reached various parts of the empire . At Chang ' an , Li Yuan responded by having Emperor Gong yield the throne to him , establishing Tang Dynasty as its Emperor Gaozu . At Luoyang , seven of the leading officials declared another grandson of Emperor Yang , Yang Tong the Prince of Yue , emperor , and Yang Tong was recognized as Sui ' s emperor by most of the commanderies that still recognized Sui sovereignty . With both the Sui administration at Luoyang and Li Mi fearing Yuwen ' s northward advancement , they formed a temporary alliance in which Li Mi recognized Yang Tong as his sovereign . After Li Mi repelled Yuwen , however , Wang , who opposed the alliance , seized power from the other officials and became regent , and the alliance with Li Mi was broken . Later that year , in a surprise attack , Wang defeated Li Mi , forcing Li Mi to flee to Tang . Li Mi was later killed by Tang forces when he tried to reestablish his own independence . Meanwhile , after Xue Ju died in early 618 and was succeeded by his son Xue Rengao , the Tang general Li Shimin the Prince of Qin ( Emperor Gaozu ' s son ) defeated and killed Xue Rengao , annexing his Qin state into Tang . At the same time , Dou Jiande further consolidated his holdings north of the Yellow River and killed Yuwen ( who had poisoned Yang Hao and declared himself Emperor of Xu ) , but was unable to get Luo Yi to submit to him , and Luo subsequently submitted to Tang . Around the same time , Zhu , facing heavy resistance from the populace against his cruelty , vacillated between submitting to Yang Tong ' s Sui regime and Tang , eventually surrendering to Sui . In summer 619 , Wang had Yang Tong yield the throne to him , ending Sui and establishing a new state of Zheng as its emperor . Reintegration under Tang . Around the same time , Li Gui ' s official An Xinggui ( 安興貴 ) captured Li Gui in a coup and surrendered the state to Tang . Tang , however , was facing a threat on a different front , as Liu Wuzhou made a major attack south , taking over much of modern Shanxi , which Tang had controlled , and appearing poised to further attack Tang ' s capital Chang ' an . Around the same time , the lower Yangtze region , which had been in a state of confusion ever since Emperor Yang ' s death , was coalescing around three different competing figures — the former Sui official Shen Faxing , who declared himself the Prince of Liang and controlled much of the territory south of the Yangtze ; the rebel leader Li Zitong , who controlled Jiangdu and the surrounding regions , declaring himself the Emperor of Wu ; and Du Fuwei , who submitted to Tang and was created the Prince of Wu . In late 619 , Tang forces , commanded by Li Shimin , began a counterattack against Liu Wuzhou . By summer 620 , Li Shimin had defeated Liu , who abandoned his territory and fled to Eastern Tujue . His Dingyang state was integrated into Tang . After defeating Dingyang , Li Shimin had his sights set on Zheng . He advanced to the Zheng capital Luoyang and put it under siege . Many Zheng cities surrendered to Tang , forcing Wang to seek aid from Dou Jiande ' s Xia state . Dou , reasoning that if Tang destroyed Zheng , his own Xia would be cornered , agreed , and he advanced south toward Luoyang , seeking to lift the siege . Around the same time , Du ( now using the name Li Fuwei , having been granted the imperial surname of Li by Emperor Gaozu ) defeated Li Zitong , who in turn defeated Shen , forcing him to commit suicide . Li Zitong now had Shen ' s former territory , while Li Zitong ' s former territory was held by Li Fuwei in Tang ' s name . In spring 621 , with Dou approaching , Li Shimin advanced east to the important Hulao Pass and held position there . When Dou engaged him , he defeated Dou and captured him . In fear , Wang surrendered . Emperor Gaozu executed Dou while exiling Wang ( although Wang was subsequently killed by the Tang general Dugu Xiude ( 獨孤修德 ) , whose father had been executed by Wang ) . Wang ' s Zheng state and Dou ' s Xia state were annexed by Tang , although former Xia territory soon rose under the leadership of Dou ' s general Liu Heita , who declared himself the Prince of Handong , and modern Shandong , which had been controlled by the agrarian leader Xu Yuanlang but had successively submitted to Zheng and then to Tang , rose as well under Xu , who declared himself the Prince of Lu . Also in 621 , Emperor Gaozu ' s nephew Li Xiaogong the Prince of Zhao Commandery attacked Xiao Xian ' s Liang state , putting the Liang capital Jiangling under siege . Xiao , not realizing that relief forces were approaching , surrendered , and most of his state was annexed by Tang , while some of Xiao ' s army submitted to Lin Shihong . Around the same time , Li Fuwei defeated Li Zitong , forcing Li Zitong ' s surrender , and Li Zitong ' s Wu state was also annexed by Tang . In spring 622 , Li Shimin defeated Liu Heita , forcing Liu to flee to Eastern Tujue , but Liu returned later that year with Eastern Tujue aid , reoccupying the former Xia territory . In winter 622 , Li Shimin ' s older brother Li Jiancheng the Crown Prince defeated Liu again , and in spring 623 , Liu , in flight , was betrayed by his official Zhuge Dewei ( 諸葛德威 ) and executed by Li Jiancheng . Earlier , Lin had died , and his Chu state dissipated , with the cities gradually submitting to Tang , and soon after Liu ' s death , Xu , who had repeatedly been defeated by Tang forces , was also killed in flight . By this point , other than Liang Shidu and Gao Kaidao in the extreme north , China was largely reunited , if somewhat nominally , under Tang rule . In fall 623 , however , with Li Fuwei at Chang ' an , Li Fuwei ' s lieutenant Fu Gongshi rebelled at Danyang , declaring himself the Emperor of Song and controlling the territory formerly under Li Fuwei ' s control . By 624 , Li Xiaogong had defeated and killed Fu , reintegrating Song territory into Tang , while Gao , faced with a coup led by his subordinate Zhang Jinshu ( 張金樹 ) , committed suicide , and his Yan state was also integrated into Tang . Meanwhile , Liang Shidu , protected by Eastern Tujue aid , was holding up against Tang attacks , and Tang itself was continually harassed by Eastern Tujue raids . After Li Shimin ambushed and killed Li Jiancheng and another brother , Li Yuanji the Prince of Qi in 626 and effectively forced Emperor Gaozu to yield the throne to him ( as Emperor Taizong ) , however , Tang began to turn the situation around . By 628 , with Eastern Tujue in internal turmoil due to disagreements between the Jiali Khan Ashina Duobi ( Ashina Duojishi ' s younger brother ) and the subordinate Tuli Khan , Ashina Shibobi ( 阿史那什鉢苾 , Ashina Duojishi ' s son ) , it was no longer able to protect Liang Shidu , and under Tang siege , Liang Shidu ' s cousin Liang Luoren ( 梁洛仁 ) killed Liang Shidu and surrendered . All of China was now under the rule of Emperor Taizong .