出身

沮渠原是匈奴官名，分為左沮渠與右沮渠。沮渠蒙遜出身匈奴貴族，為盧水胡領袖。

生平

復仇起兵

沮渠蒙遜博覽史籍，知曉天文，才智出眾又有謀略，為人圓滑又靈活變通，故前秦將領如梁熙及呂光都對其才能既感驚異，亦生畏懼。沮渠蒙遜知道後亦常飲酒出遊，故作低調。前秦亡後，蒙遜一族依附呂光建立的後涼。397年，蒙遜伯父後涼尚書沮渠羅仇和三河太守沮渠麴粥隨從後涼進攻西秦的乞伏乾歸，呂光弟呂延輕敵，兵敗被殺，後涼軍被迫撤退。呂光以敗軍之罪殺羅仇、麴粥二人，蒙遜在宗族聚集參加二人喪禮的機會舉眾叛涼，斬後涼中田護軍馬邃及臨松令井祥與眾盟誓，十日之間就招合了萬多人，屯兵金山。同年，蒙遜堂兄沮渠男成擁立段業稱涼州牧，建北涼，蒙遜附之，獲授鎮西將軍、張掖太守。

屢見智謀

398年，蒙遜深知西郡戰略價值高，遂大力支持段業進攻該郡的決定，並受命進攻。然而蒙遜攻郡城十餘日不下，改為引水灌城，終逮獲太守呂純而返，晉昌郡王德及敦煌郡孟敏戰後皆向北涼歸降。蒙遜以功封為臨池侯。同年後涼張掖守將呂弘率眾棄城東歸，蒙遜以「歸師勿遏，窮寇弗追」為理反對段業追擊，但段業不聽，終為呂弘所敗，段業更因蒙遜才得安全撤退，因而嘆道：「我沒有聽從子房的話，才會有此結果！」後蒙遜又反對段業以將領臧莫孩擔任新建西安城的太守，稱臧莫孩「勇而無謀，知進忘退」，必會失敗。段業又不聽，不久臧莫孩就被後涼呂纂擊敗。天璽元年（399年），段業稱涼王，以蒙遜為尚書左丞。不久，後涼太子呂紹及呂纂來攻，段業請得南涼禿髮烏孤派楊軌等救援，就打算迎擊，蒙遜就說：「楊軌恃著騎兵戰力強，有伺機圖謀我們的意圖。而呂紹和呂纂在死地，肯定會與我們決戰以求生。拒絕對戰將有如泰山般安穩，出戰則像疊起的蛋一樣危險。」段業同意，遂按兵拒絕接戰，後涼軍沒有辦法，亦退兵。

兵變登位

雖然蒙遜屢次建言協助段業，但卻害怕對方容不下自己，所以每每特意不顯露自己的智謀。段業也畏懼蒙遜的能力，故此調蒙遜為臨池太守，改以門下侍郎馬權為張掖太守。馬權得段業信任和重用，其人亦有過人軍事謀略，卻輕視並常欺侮蒙遜，令蒙遜對他又恨又怕，於是向段業進言中傷馬權，卻令段業將馬權殺死。蒙遜隨後向沮渠男成建議除去段業，改奉男成為主，但被男成拒絕。蒙遜心中不安，自求外任西安太守，也得段業批准。

不過蒙遜天璽三年（401年）四月約男成一同去祭告蘭門山（甘肅省山丹縣西南）時，暗中派人告訴段業說男成準備發動變亂，段業斬男成，男成死前對段業說：「蒙遜早就和臣說過他要叛亂了，只是臣以兄弟緣故才不說出來。蒙遜以臣還在，怕部眾不聽從他，于是約臣與其祭山，反派人誣告臣。臣若果死了，蒙遜肯定很快就起兵了。請假稱臣死了，宣告臣的罪行，蒙遜肯定會起兵叛亂，而臣立即就會討伐他，必會成功。」段業不聽。蒙遜以此為藉口出兵攻段，並進屯侯塢，段業急派右將軍田昂、武威將軍梁中庸反擊蒙遜，田昂、梁中庸至侯塢反降蒙遜，五月，蒙遜大軍抵張掖（今甘肅張掖西北），田昂侄子田承愛開城門內應，蒙遜入城，殺段業，遂稱大都督、大將軍、涼州牧、張掖公，改年號永安。

後秦亦在永安二年（402年）任命沮渠蒙遜為鎮西將軍、沙州刺史、西海侯。蒙遜登位後提拔人才，得文武官員支持。

攻奪姑臧

蒙遜曾經送子沮渠奚念到南涼做人質，想與其結好，然而南涼主禿髮利鹿孤嫌奚念年幼，要求改以蒙遜弟沮渠挐為質。蒙遜寫信表示不願，竟惹怒利鹿孤並遭進攻，蒙遜唯有答應利鹿孤的要求。永安七年（407年），禿髮傉檀率兵五萬進攻蒙遜，蒙遜於均石擊敗傉檀，並進攻南涼西郡太守楊統。永安十年（410年），蒙遜因之前南涼枯木及胡康攻掠臨松而攻南涼，至顯美強遷數千戶人退兵。傉檀率兵追擊，並在窮泉追上蒙遜，蒙遜大敗傉檀，更乘勝攻至姑臧，萬多戶姑臧人民向蒙遜歸降。蒙遜隨後接受傉檀求和，遷八千多戶人離開。傉檀不久就遷都至樂都，焦朗等人乘勢據姑臧自立，蒙遜遂率三萬兵進攻，奪取了姑臧。412年，蒙遜遷都姑臧，稱河西王，改元玄始。

消滅西涼

西涼在沮渠蒙遜殺段業登位前一年自立，蒙遜曾於永安十一年（411年）輕兵襲擊西涼，西涼君主李暠閉門拒戰，蒙遜撤兵時更被西涼世子李歆擊敗。至玄始六年（417年）李歆即位，蒙遜命張掖太守沮渠廣宗詐降西涼，李歆中計出兵迎接但及後卻發現蒙遜所領的三萬伏兵而撤走，蒙遜追擊卻在鮮支澗一戰中大敗予李歆。蒙遜一度想重結敗兵再戰，但為沮渠成都勸止，在增築建康城後班師。玄始九年（420年），李歆乘蒙遜攻西秦浩亹的機會進攻，蒙遜聞訊時正自浩亹回師至川巖，於是發布浩亹已下，即將進攻黃谷的假消息，讓李歆以為蒙遜仍在外，實質正暗中回援。李歆果然繼續進攻，兩軍遂於懷城決戰，李歆兵敗但不肯撤退，堅持再戰，於是在蓼泉再敗並被殺。蒙遜因而乘勢攻陷西涼都城酒泉，滅亡了西涼。次年，蒙遜率軍進攻李恂領導之西涼殘餘勢力所據的敦煌，成功攻陷，徹底滅亡西涼勢力。

交結宋魏

朱齡石滅蜀後曾與蒙遜有使者往來，蒙遜亦上表表示其臣服於東晉，晉廷亦授予涼州刺史。玄始十年（421年），把持東晉軍政的劉裕代晉建南朝宋後，於十月任命沮渠蒙遜為使持節、散騎常侍、都督涼州諸軍事、鎮軍大將軍、開府儀同三司、涼州刺史、張掖公。玄始十二年（423年）二月，蒙遜遣使南朝宋，宋廷進蒙遜侍持節、開府、侍中、都督涼秦河沙四州諸軍事、驃騎大將軍、領護匈奴中郎將、西夷校尉、涼州牧，河西王。玄始十五年（426年）五月又獲改授車騎大將軍。承玄四年（431年），蒙遜又曾命人出使北魏，更派兒子沮渠安周入魏，北魏遂命其為假節，侍中，都督涼州西域羌戎諸軍事，太傅，行征西大將軍，涼州牧，涼王。

義和三年（433年），蒙遜去世，享年六十六，諡武宣王，廟號太祖。因他生前所立繼承人沮渠菩提年幼，貴族擁立其年長之子沮渠牧犍繼位。

性格特徵

沮渠蒙遜有軍事才能，故屢次向段業提供意見助其解兵厄，亦讓其國能立於河西諸國間。登位後，蒙遜伯父中田護軍沮渠親信及臨松太守沮渠孔篤驕橫奢侈，侵害人民，蒙遜說：「禍亂我國家的就是兩位伯父呀，還怎治理百姓呀！」於是命二人自殺《晉書·載記第二十九》：「蒙遜伯父中田護軍親信、臨松太守孔篤並驕奢侵害，百姓苦之。蒙遜曰：『亂吾國者，二伯父也，何以綱紀百姓乎！』皆令自殺。」。不過他用計陷害堂兄男成，接著攻殺他推舉的段業，令《晉書》評價他「見利忘義，苞禍滅親。」蒙遜知劉裕滅後秦的消息後十分憤怒，門下校郎劉詳其時有事報告，蒙遜卻回應：「你知道劉裕入關，竟敢這樣得意！」就將劉詳殺了，亦見其嚴酷殘暴一面《晉書·載記第二十九·沮渠蒙遜傳》：「蒙遜聞劉裕滅姚泓，怒甚。門下校郎劉祥言事于蒙遜，蒙遜曰：『汝聞劉裕入關，敢研研然也！』遂殺之。其峻暴如是。」。

據《晉書》所載，蒙遜頗信天象，並寫其多次憑天象指引而勝利《晉書·載記第二十九》：「太史令劉梁言于蒙遜曰：『辛酉，金也。地動于金，金動刻木，大軍東行無前之徵。』時張掖城每有光色，蒙遜曰：『王氣將成，百戰百勝之象也。』遂攻禿髮西郡太守楊統於日勒。」《晉書·載記第二十九》：「太史令張衍言于蒙遜曰：『今歲臨澤城西當有破兵。』蒙遜乃遣其世子政德屯兵若厚塢。蒙遜西至白岸，謂張衍曰：『吾今年當有所定，但太歲在申，月又建申，未可西行。且當南巡，要其歸會，主而勿客，以順天心。計在臨機，慎勿露也。』遂攻浩亹，而蛇盤于帳前。蒙遜笑曰：『前一為騰蛇，今盤在吾帳，天意欲吾迴師先定酒泉。』燒攻具而還，次于川巖。聞李士業徵兵欲攻張掖，蒙遜曰：『入吾計矣。但恐聞吾迴軍，不敢前也。兵事尚權。』」《晉書·載記第二十九》：「（蒙遜）顧謂左右曰：『古之行師，不犯歲鎮所在。姚氏舜後，軒轅之苗裔也。今鎮星在軒轅，而裕滅之，亦不能久守關中。』」。亦有載蒙遜曾祭祀西王母寺，並命中書侍郎張穆為寺內的《玄石神圖》作賦，銘於寺前；蒙遜又曾派世子沮渠興國到南朝宋借《周易》等書，又曾向南朝宋司徒王弘求《搜神記》《宋書·卷九十八》：「世子興國遣使奉表，請《周易》及子集諸書，太祖並賜之，合四百七十五卷。蒙遜又就司徒王弘求《搜神記》，弘寫與之。」。沮渠蒙遜曾在母車太后病重時引咎于己，同時大赦死罪以下，車太后仍然去世。當旱災時，他也有同樣舉動，次日就下大雨了。

逸事

蒙遜亦信佛，其時有一名自西域東來的僧人曇無讖在涼州譯經，又「以男女交接之術教授婦人」，時蒙遜諸女及子媳都信奉他。曇無讖亦通術數和咒術，屢次準確說出其他國家的事，沮渠蒙遜遂奉曇無讖為國師，每以國事諮之。後北魏聽聞曇無讖的事跡，要求蒙遜將曇無讖送到北魏，蒙遜不肯，及後還將他殺了。

家庭

妻

• 孟王后

子女

• 沮渠政德，413年立為繼承人，423年對柔然軍作戰陣亡

• 沮渠興國，423年立為繼承人，429年被西秦天王乞伏暮末俘虜拘押，431年卒

• 沮渠牧犍，433年立為繼承人，後為天王

• 沮渠菩提，沮渠興國同母弟，429年立為繼承人，433年廢黜

• 沮渠無諱，後為天王

• 沮渠安周，後為天王

• 沮渠儀德

• 沮渠秉，444年被北魏太武帝所殺

• 沮渠董來

• 沮渠奚念，曾被派去南涼為質子，為禿髮利鹿孤拒絕

• 興平公主，後為北魏太武帝右昭儀，447年被賜死

• 某女，沮渠牧犍姐

Under Later Liang and Duan Ye

Juqu Mengxun was born in 368, while the area that would later be his domain was under the rule of Former Liang, but little is known about his early years. He was of Xiongnu ancestry, and it was said that his ancestors served as the left Juqu (an office title of unclear responsibility) for Xiongnu Chanyus, and so they started using Juqu as the family name. Later, during Former Qin and Later Liang rule, Juqu Mengxun became known for broad knowledge in history and military tactics and thought to be both humorous and full of strategies, and became feared by the Former Qin governor Liang Xi (梁熙) and the Later Liang emperor Lü Guang, and so he tried to divert attention from himself by drinking heavily and spending time on frivolous matters.

In 397, Lü Guang sent his brother Lü Yan (呂延) on an attack against Western Qin, but Lü Yan was killed in a trap set by the Western Qin prince Qifu Gangui. Juqu Mengxun's uncles Juqu Luochou (沮渠羅仇) and Juqu Quzhou (沮渠麴粥) were Lü Yan's assistants, and in light of Lü Yan's death, Lü Guang believed false accusations against them and executed them. Juqu Mengxun escorted their caskets back to their home territory of Zhangye (張掖, in modern Zhangye, Gansu) and then persuaded the various Xiongnu tribes to rise against Later Liang. Initially, he was defeated by Lü Guang's son Lü Zuan and fled into the mountains, but he was soon joined in rebellion by his cousin Juqu Nancheng (沮渠男成), who sieged Jiankang (建康, also in modern Zhangye) and persuaded Duan Ye the governor of Jiankang Commandery to accept leadership of the rebels, establishing Northern Liang. Soon, Lü Guang came under the greater threat of a rebellion by Guo Nen (郭黁) and recalled Lü Zuan to face that threat, and Duan Ye's nascent state survived. Juqu Mengxun joined Duan Ye, and was made a major general of the state. In 398, Duan Ye sent him on an expedition against Lü Guang's nephew Lü Chun (呂純), and Juqu Mengxun captured Lü Chun, causing all remaining Later Liang cities west of Zhangye to submit to Northern Liang, further enlarging Northern Liang territory. Duan Ye therefore created Juqu Mengxun the Marquess of Linchi. Lü Guang's son Lü Hong (呂弘) soon abandoned Zhangye, and Duan Ye moved his capital to Zhangye, and tried to further pursue Lü Hong against Juqu Mengxun's advice. Lü Hong defeated him and nearly killed him, but Juqu Mengxun saved Duan Ye. In 399, when Duan Ye claimed the title of Prince of Liang, he made Juqu Mengxun one of his two prime ministers, sharing responsibilities with Liang Zhongyong (梁中庸). Later that year, when Northern Liang was under attack by Lü Guang's crown prince Lü Shao and Lü Zuan, it was at Juqu Mengxun's suggestion that Duan Ye refused to engage, forcing Lü Shao and Lü Zuan to retreat when Southern Liang relief forces under Tufa Lilugu arrived. In 400, when the general Wang De (王德) rebelled, Duan Ye sent Juqu Mengxun to attack him, and Juqu Mengxun defeated him and, while he fled, captured his wife and children.

By 401, however, Duan Ye was heavily apprehensive of Juqu Mengxun's strategies and abilities, and he considered sending Juqu Mengxun far away. Juqu Mengxun, knowing Duan Ye's suspicions, tried to hide his ambitions. However, at the same time, because he was often insulted by another official that Duan Ye heavily relied on, Ma Quan (馬權), he falsely accused Ma of treason, and Duan Ye killed Ma. Juqu Mengxun then told Juqu Nancheng that he felt that Duan Ye lacked abilities and was an inappropriate ruler, trying to persuade Juqu Nancheng to rise against Duan Ye. When Juqu Nancheng refused, Juqu Mengxun requested to leave the capital to be the governor of Xi'an Commandery (西安, also in modern Zhangye), and Duan Ye agreed. Juqu Mengxun then set a trap for both Juqu Nancheng and Duan Ye—he made an appointment with Juqu Nancheng to offer sacrifices to the god of Lanmen Mountain (蘭門山, near Zhangye) on a vacation day, but submitting a false report through the official Xu Xian (許咸) that Juqu Nancheng was set to rebel and would start the rebellion on a day that he requested permission to sacrifice to the god of Lanmen Mountain. When Juqu Nancheng requested Duan Ye for such permission, Duan Ye arrested him and ordered him to commit suicide. Juqu Nancheng, who had realized Juqu Mengxun's plan by this point, told Duan Ye that this was a sign that Juqu Mengxun was about to rebel and that he should keep Juqu Nancheng alive, and then when Juqu Mengxun rebels he could counterattack. Duan Ye, not believing in Juqu Nancheng, executed him. Juqu Mengxun then cited Duan Ye's execution of Juqu Nancheng to ask his people to rise against Duan Ye, and the people indeed rose in rebellion, because of the high regard they had for Juqu Nancheng. The rebels quickly arrived at Zhangye, and it fell. Despite Duan Ye's pleas, Juqu Mengxun executed him. The Northern Liang officials all endorsed Juqu Mengxun to take over the throne, and he took throne with the title Duke of Zhangye.

Early reign

Juqu Mengxun, having taken the ducal title, promoted a number of officials who were considered capable, and it was said that the people of his state were pleased. He also nominally submitted to the Later Qin emperor Yao Xing as a vassal, although remaining in reality independent. However, he immediately faced the crisis that his Jiuquan (酒泉) and Liangning (涼寧) Commanderies (roughly modern Jiuquan, Gansu) rebelled against him and joined Western Liang. He became fearful, and he sent his brother Juqu Ru (沮渠挐) the Marquess of Dugu and official Zhang Qian (張潜) to meet Yao Xing's uncle Yao Shuode (姚碩德), who had just recently sieged Later Liang's capital Guzang (姑臧, in modern Wuwei, Gansu) and forced the Later Liang emperor Lü Long to submit, offering to surrender his state to Later Qin. Yao Shuode was pleased, but upon return to Northern Liang, while Zhang recommended such surrender, Juqu Ru argued against it, and Juqu Mengxun, while remaining nominally a Later Qin vassal, executed Zhang and never actually surrendered his state. He also tried to make peace with Southern Liang's prince Tufa Lilugu, initially sending his son Juqu Xi'nian (沮渠奚念) as a hostage to Southern Liang, but Tufa Lilugu rejected Juqu Xi'nian, stating that he was too young to be a meaningful hostage and demanding Juqu Ru instead. After initially refusing, Juqu Mengxun gave in to Southern Liang demands after Tufa Lilugu defeated him in battle.

In 402, with Guzang under a severe famine, Juqu Mengxun attacked Later Liang, causing Lü Long to seek aid from Southern Liang, but before Southern Liang forces could arrive, Lü Long defeated Juqu Mengxun, and Juqu Mengxun made peace with Lü Long, offering him food for famine relief.

Around the new year 403, Liang Zhongyong, who continued to be a key official after Juqu Mengxun took over for Duan Ye, fled from his domain and joined Western Liang's prince Li Gao. Rather than killing Liang's wife and children as might be expected, Juqu Mengxun sent them to Liang, commenting, "I treated Liang like a brother, but he did not trust me. He did not betray me, but himself; I do not mind losing a man."

Later that year, because Juqu Mengxun and Tufa Lilugu were constantly attacking him and draining his state's resources, Lü Long felt he could not maintain his state any more, and he surrendered his state (now constiting of little more than Guzang) to Later Qin. He also persuaded the Later Qin general Qi Nan (齊難) to attack Juqu Mengxun, but Juqu Mengxun repelled Qi's attack and then made peace with Qi. Juqu Mengxun sent Juqu Ru (who must have somehow been returned from Southern Liang by this point) to the Later Qin capital Chang'an to declare his submission to Yao Xing. Later that year, having received reports that his two uncles and generals Juqu Qinxin (沮渠親信) and Juqu Kongdu (沮渠孔篤) were corrupt and harmful to the people, he forced to commit suicide. Meanwhile, he accepted the title that Yao Xing created him, the Marquess of Xihai, to show submission, despite his initial displeasure that Tufa Lilugu's brother and successor Tufa Rutan was created a duke while he was only created a marquess.

In 405, Li Gao moved his capital from Dunhuang (敦煌, in modern Dunhuang, Gansu) to Jiuquan, to be closer to Zhangye to exert pressure on Juqu Mengxun.

In spring 406, Tufa Rutan launched a major attack on Northern Liang, but Juqu Mengxun was able to hold Zhangye, forcing Tufa Rutan to withdraw. In fall 406, Juqu Mengxun made a surprise attack on Jiuquan, initially defeated Li Gao, but he could not successfully siege Jiuquan and was forced to withdraw.

In fall 407, Tufa Rutan made another attack on Northern Liang, but Juqu Mengxun was able to defeat him.

In 410, Tufa Rutan and his brother Tufa Juyan (禿髮俱延) launched successive attacks on Northern Liang, and Juqu Mengxun was not only able to repel them, but then proceeded to siege Guzang (where Tufa Rutan had moved his capital after receiving it as a bestowmen from Yao Xing in 406). The people of Guzang, because Tufa Rutan had previously carried out massive executions after a failed rebellion, collapsed in fear, and more than 10,000 households surrendered to Northern Liang. Tufa Rutan, apprehensive of both Juqu Mengxun and a rebellion by Zhequ Qizhen (折屈奇鎮) in the south, made peace with Juqu Mengxun and moved his capital back south to Ledu (樂都, in modern Haidong Prefecture, Qinghai). As soon as he left Guzang, however, Hou Chen (侯諶) and Jiao Lang (焦朗) seized control of Guzang and nominally submitted to Juqu Mengxun, although they held Guzang themselves. In fall 410, Juqu Mengxun attacked Western Liang and defeated Li Gao's heir apparent Li Xin and captured the Western Liang general Zhu Yuanhu (朱元虎), and he subsequently made peace with Li Gao when Li Gao ransomed Zhu with silver and gold.

In spring 411, with Jiao Lang still holding Guzang, Juqu Mengxun sieged Guzang and captured him, but pardoned him. He left Juqu Ru in command at Guzang and then attacked Southern Liang, putting Ledu under siege, and only withdrew after Tufa Rutan sent his son Tufa Anzhou (禿髮安周) as a hostage. Tufa Rutan soon counterattacked, however, and initially was successful, but Juqu Mengxun trailed Tufa Rutan's forces and defeated him, again putting Ledu under siege and forcing Tufa Rutan to send another son, Tufa Ran'gan (禿髮染干) as a witness before withdrawing. In fall 411, Juqu Mengxun made a surprise attack on Western Liang, but was unsuccessful, and as he ran out of food supplies and withdrew, Li Gao sent Li Xin to attack him, defeating him.

In winter 412, Juqu Mengxun moved the capital from Zhangye to Guzang, and he claimed the greater title of Prince of Hexi.

Middle reign

In 413, Juqu Mengxun created his son Juqu Zhengde (沮渠政德) heir apparent. In the summer of that year, he repelled another attack from Tufa Rutan, and then again put Ledu under siege for 20 days, but could not capture it. He renewed the attack when Tufa Rutan's general Tufa Wenzhi (禿髮文支) surrendered to him, forcing Tufa Rutan to send Tufa Juyan as a hostage to him.

Also in 413, while Juqu Mengxun was sleeping, his eunuch Wang Huaizu (王懷祖) tried to assassinate him, but only hurt his foot. Juqu Mengxun's wife Princess Meng arrested Wang and had him beheaded. Also in 413, Juqu Mengxun's mother Lady Che died.

With Western Qin having destroyed Southern Liang in 414, Northern Liang and Western Qin began to have a series of wars, with Juqu Mengxun largely winning these battles against Western Qin's prince Qifu Chipan. In 416, after an inconclusive battle, Northern Liang and Western Qin entered into peace.

In 417, Juqu Mengxun tried to lay a trap for Li Xin (who had succeeded Li Gao after Li Gao's death that year) by having his general Juqu Guangzong (沮渠廣宗) pretending to surrender to Western Liang, while Juqu Mengxun lay in wait. However, Li Xin realized the trap and withdrew, and as Juqu Mengxun gave chase, Li Xin defeated him.

That year, Juqu Mengxun became fearful and angry when he heard that the Jin general Liu Yu had destroyed Later Qin and seized its territory, probably in fear that Liu Yu would next advance against his state. When his official Liu Xiang (劉祥) was making a report to him with a smile, Juqu Mengxun angrily stated, "How do you dare to smile upon hearing that Liu Yu had entered Hangu Pass!" and beheaded Liu Xiang. (This is despite Juqu Mengxun having made an overture in 415 agreeing to submit to Jin as a vassal.) His fears appeared to subside after Liu Yu left former Later Qin territory late in 417, and dissipate completely when the Xia emperor Helian Bobo crushed troops under Liu Yu's son Liu Yizhen (劉義真) in 418.

In 418, Juqu Mengxun made an attack on Western Liang, but Li Xin refused to engage him, and he withdrew. Later that year, he submitted to Jin as a vassal.

In 420, Juqu Mengxun set another trap for Li Xin. He pretended to attack Western Qin's city Haomen (浩亹, in modern Haidong Prefecture, Qinghai), but once reaching Haomen, immediately withdrew and hid his army at Chuanyan (川巖, near Zhangye). Li Xin, believing wrongly that Juqu Mengxun's defenses were down, decided to attack Zhangye, against the advice of Song Yao and Zhang Tishun, as well as his mother Princess Dowager Yin. As he approached Zhangye, Juqu Mengxun intercepted him and defeated him. His generals then advised him to quickly withdraw to Jiuquan, but Li Xin, stating that he had disobeyed his mother and would only be able to see her again after a victory, engaged Juqu Mengxun again, suffering an even greater defeat, and he was killed in battle. Juqu Mengxun quickly captured Jiuquan and most of Western Liang territory. He largely maintained a policy of trying to pacify the Western Liang people and incorporating capable Western Liang officials into his administration, including Li Gao's half-brother Song Yao (宋繇). In winter 420, Li Xin's brother Li Xun seized Dunhuang and tried to reestablish Western Liang rule, and Juqu Mengxun initially sent Juqu Zhengde to siege Dunhuang. In spring 421, he attacked Dunhuang himself, and when Li Xun tried to surrender, he refused. Li Xun's official Song Cheng (宋承) rebelled and offered the city to him, and Li Xun committed suicide, ending Western Liang; contrary to the pacification policy he carried out at Jiuquan, Juqu Mengxun slaughtered the populace of Dunhuang.

With Western Liang destroyed, Juqu Mengxun renewed his attacks against Western Qin, and while his initial attacks were repelled, his attacks had a draining effect on Western Qin, whose strength began to be sapped. At some point, he also encouraged Tufa Rutan's crown prince Tufa Hutai (禿髮虎台) to rebel against Western Qin, promising to lend him two commanderies and troops, but after Tufa Hutai's plot, which also included his sister Princess Tufa (Qifu Chipan's wife), was discovered, Qifu Chipan had Tufa Hutai and Princess Tufa executed. Some members of the Tufa clan fled to Northern Liang.

In 421, the general Tang Qi (唐契), a former Western Liang general and brother-in-law to Li Xin, rebelled at his post of Jinchang (晉昌, in modern Jiuquan, Gansu), and not until 423 did Juqu Zhengde defeat Tang, but Tang and his brother Tang He (唐和) and nephew Li Bao (李寶, Li Xin's son) fled to Yiwu (伊吾, in modern Kumul Prefecture, Xinjiang) and held out there.

Also in 423, Juqu Mengxun sent tributes to Jin's successor state, Liu Song, which Liu Yu had established in 420. Liu Yu's son Emperor Shao of Liu Song affirmed Juqu Mengxun's title of Prince of Hexi. In fall of that year, when Rouran attacked Northern Liang, Juqu Mengxun sent Juqu Zhengde to fight Rouran, but Juqu Zhengde was defeated and killed. Juqu Mengxun then created his next son Juqu Xingguo (沮渠興國) as heir apparent.

In 426, a decisive battle would largely end Western Qin as a threat to Northern Liang. Qifu Chipan and his crown prince Qifu Mumo were launching a major attack on Northern Liang. Juqu Mengxun sent messengers to persuade the Xia emperor Helian Chang (Helian Bobo's son and successor) to make a surprise attack on the Western Qin capital Fuhan (枹罕, in modern Linxia, Gansu). Helian Chang, in response, sent his general Hulu Gu (呼盧古) to attack Wanchuan and Wei Fa (韋伐) to attack Nan'an (南安, in modern Dingxi, Gansu), and while Western Qin was able to hold Wanchuan, Nan'an fell, at great loss. In winter 426, Xia forces commanded by Hulu and Wei attack Fuhan, forcing Qifu Gangui to move the capital to Dinglian (定連, also in Linxia), and Hulu and Wei then captured another important Western Qin city, Xiping (西平, in modern Xining, Qinghai), and while they then withdrew, Western Qin had been dealt a major blow. Later that year, with Emperor Taiwu of Northern Wei having in turn defeated Helian Chang in battle, capturing Chang'an and nearly capturing the Xia capital Tongwan (統萬, in modern Yulin, Shaanxi) as well, Juqu Mengxun sent messengers to Northern Wei offering to submit as a vassal.

In 428, when Qifu Chipan died and was succeeded by Qifu Mumo, Juqu Mengxun made a major attack on Western Qin. Qifu Mumo sent back his general Juqu Chengdu (沮渠成都), whom Qifu Chipan captured in 422, to seek peace, and they entered into a peace agreement. However, just several months later, Juqu Mengxun renewed his attacks on Western Qin.

Late reign

In 429, Juqu Mengxun launched another major attack on Western Qin, but during the campaign, Juqu Xingguo was captured, and Juqu Mengxun was forced to withdraw, after his forces, aligned also with Tuyuhun forces commanded by Murong Muliyan (慕容慕利延), the brother of the khan Murong Mugui (慕容慕璝). He soon sent a large amount of grain to Qifu Mumo, requesting to ransom Juqu Xingguo, but Qifu Mumo refused, so Juqu Mengxun created Juqu Xingguo's younger brother, by the same mother, Juqu Puti (沮渠菩提), to be heir apparent. (Qifu Mumo kept Juqu Xingguo as an official and married a sister to him.)

In 431, with Xia's emperor Helian Ding (Helian Chang's brother and successor after Helian Chang was captured by Northern Wei in 428) having first destroyed Western Qin and killed Qifu Mumo and then having been defeated and captured by Murong Mugui), Juqu Mengxun, now with his territory directly in contact with Northern Wei, sent his son Juqu Anzhou to Northern Wei as a hostage to show his loyalty. In response, Northern Wei's Emperor Taiwu sent his official Li Shun (李順) to Northern Liang to bestow a number of high titles, including the title of Prince of Liang.

By 432, Juqu Mengxun, in his old age, was said to be arbitrary and cruel, with his subjects suffering the pain henceforth. When Li Shun again arrived in his territory, he initially refused to bow down to receive the Northern Wei emperor's edict, but upon Li Shun's warning that such disrespect will be punished, did so. In 433, he grew ill, and his nobles and officials believed Juqu Puti to be too young to succeed him, and so deposed Juqu Puti and replaced him as heir apparent with his older brother Juqu Mujian. Juqu Mengxun soon died, and Juqu Mujian succeeded him.

Era names

• Yong'an (永安 yǒng ān) 401–412

• Xuanshi (玄始 xuán shǐ) 412–428

• Chengxuan (承玄 chéng xuán) 428–430

• Yihe (義和 yì hé) 430–433

Personal information

• Mother

　• Lady Che (d. 413)

• Wife

　• Princess Meng

• Children

　• Juqu Zhengde (沮渠政德), the Heir Apparent (created 413, killed in battle by Rouran forces 423)

　• Juqu Xingguo (沮渠興國), the Heir Apparent (created 423), later captured and detained by Western Qin's prince Qifu Mumo 429 (d. 431)

　• Juqu Puti (沮渠菩提), the Heir Apparent (created 429, deposed 433)

　• Juqu Mujian (沮渠牧犍), the Heir Apparent (created 433), later prince

　• Juqu Wuhui (沮渠無諱), later prince

　• Juqu Anzhou (沮渠安周), later prince

　• Juqu Yide (沮渠儀德)

　• Juqu Bing (沮渠秉) (brothers forced by Emperor Taiwu of Northern Wei to kill him 444)

　• Juqu Donglai (沮渠董來)

　• Princess Xingping, later consort to Emperor Taiwu of Northern Wei (forced to commit suicide 447)

　• Another daughter, older than Juqu Mujian