Emperor Wenzong had originally created his son Li Yong crown prince, but after Li Yong died in 838, he had been unsure whom to make his successor.

Emperor Wenzong's favorite concubine Consort Yang had recommended Li Rong, but when Emperor Wenzong consulted the chancellors, Li Jue had opposed this proposal.

Emperor Wenzong had thus, in 839, created Emperor Jingzong's youngest son Li Chengmei the Prince of Chen crown prince.

When Emperor Wenzong becomes seriously ill early in 840, he has his trusted eunuchs Liu Hongyi and Xue Jileng summon the chancellors Yang Sifu and Li Jue to the palace, intending to entrust Li Chengmei to them.

However, the powerful eunuchs Qiu Shiliang and Yu Hongzhi, who had not been not consulted in the decision, oppose Li Chengmei, and despite Li Jue's objection, forge an edict in Emperor Wenzong's name deposing Li Chengmei by claiming that Li Chengmei is too young, and creating Li Chan crown prince instead.

Subsequently, Qiu and Yu have soldiers escort Li Chan from his mansion to the palace and, after Emperor Wenzong then dies, persuade Li Chan to order Consort Yang, Li Chengmei, and Li Rong all to commit suicide.

After a short mourning period, Li Chan takes the throne as Emperor Wuzong.

The collapse of Tang's erstwhile vassal and ally the Uyghur Khaganate—which had supported the Tang Dynasty in various campaigns through the decades—is one of the first things with which Emperor Wuzong has to deal.

The Uyghur Khaganate had weakened due to internal power struggles to the point that when the Xiajiasi (Kirghiz) khan Are attacks them in 840, the Uyghur khan Yaoluoge Hesa is killed.

The Uyghur tribespeople scatter, fleeing in various directions.

One major group, under the leadership of the prince Wamosi and the nobles Chixin, Pugu, and Najiachuo, heads for the Tang border city of Tiande (in modern Hohhot, Inner Mongolia) and seeks to submit to the Tang.

The leader of another major group, the noble Yaoluoge Wuxi, claims the khan title for himself (as Wujie Khan); Wujie Khan subsequently seizes Emperor Wuzong's aunt, Princess Taihe, who had married a previous khan (Chongde Khan) and holds her hostage.

Various Uyghur remnants pillage the Tang border regions, causing much disturbance for the Tang people.

At Li Deyu's suggestion, Emperor Wuzong supplies food to the Uyghur remnants to try to calm them, while accepting Wamosi's submission.

When Wujie Khan subsequently demands that Tang turn Wamosi over to him as a traitor, Emperor Wuzong refuses.

The power of the Uyghur Khaganate had declined after the death of Tun Bagha Tarkhan death in 789, and the empire had begun to fragment.

The Tibetans had taken the area of Beshbalik, and the Karluks had captured Fu-tu valley.

The khagan bearing the title Qutlugh Bilge had died in 795, ending the Yaghlakar dynasty.

A general named had Qutlugh declared himself the new khagan, under the title Tängridä ülüg bulmïsh alp kutlugh ulugh bilgä kaghan ("Greatly born in moon heaven, victorious, glorious, great and wise Kaghan"), founding a new dynasty, the Ediz.

The Khaganate, with solid leadership once more, had averted collapse.

Qutlugh became renowned for his leadership and management of the empire but, while he consolidated the empire, he failed to restore its previous power.

The empire on his death in 808 had once again begun to fragment.

Qutlugh was succeeded by his son, who had gone on to improve trade in inner Asia.

The name of the last great khagan of the Empire is unknown, though he bore the title Kün tengride ülüg bulmïsh alp küchlüg bilge ("Greatly born in sun heaven, victorious, strong and wise").

His achievements included improved trade up with the region of Sogdiana, and on the battlefield in 821 he repulsed a force of invading Tibetans.

This khagan, who died in 824, had been succeeded by a brother, Qasar, whose murder in 832 had inaugurated a period of anarchy.

The legitimate khagan had been forced in 839 to commit suicide, and a usurping minister named Kürebir had seized the throne with the help of twenty thousand horsemen of Shato from Ordos.

A famine and an epidemic in the same year, coupled with a particularly severe winter that killed much of the livestock, had devastated the Uyghur economy.

One of nine Uyghur ministers, Kulug Bagha, rival of Kurebir, flees in the following spring, in 840, to the Kyrgyz tribe and invites them to invade from the north.

The Kyrgyz, with a force of around eighty thousand horsemen, sack the Uyghur capital at Ordu-Baliq, razing it to the ground, and capture the Uyghur Khagan, Kürebir (Hesa), who they promptly behead.

They go on to destroy other cities throughout the Uyghur Khaganate, burning them to the ground.

The center of the Yenesei Kyrgyz nation moves to Jeti-su (meaning "seven rivers, a historical name of a part of Central Asia, corresponding to the southeastern part of modern Kazakhstan.

It owes its name, meaning "seven rivers" (literally "seven waters") in Kazakh and Persian, to the rivers which flow from the south-east into Lake Balkhash.

The rise to power will brings about a spread south of the Yenesei Kyrgyz people to reach the Tian Shan and Xinjiang, bringing them into contact with the existing peoples of western China, especially Tibet.

A Lombard prince held prisoner in Taranto is in 840 freed by his partisans, brought to Benevento, and made duke.

At the same time, the Saracens take control of Taranto, exploiting the weak Lombard control to make Taranto an Arab stronghold and privileged harbor.

In the same year, an Arab fleet leaves Taranto, defeating in the Gulf of Taranto a Venetian fleet of sixty ships that had responded to a summons by the emperor Theophilos, and enters the Adriatic sea, sacking the coastal cities.

The Final Partition of the Carolingian Empire and the Outbreak of Civil War (839–840)

Throughout his long reign, Louis the Pious seeks to divide his empire fairly among his sons, adhering to Frankish traditions of partible inheritance as outlined in Salic Law. However, his decision to grant land to his youngest son, Charles the Bald, born from his second marriage to Judith of Bavaria, sparks decades of civil war among his older sons.

The Final Partition of 839: The Division at Worms

Following his vindicating victory over his last rebellious son, Louis the German, in 839, Emperor Louis the Pious divides his empire for the last time at Worms on May 30, 839:

• Lothair I → Retains Italy and the imperial title, along with all the other lands of the east, consolidating his claim as primary ruler of the empire.
• Charles the Bald → Receives all the lands of the west, ensuring a powerful Frankish kingdom that will later evolve into France.
• Louis the German → Left with only Bavaria, significantly reducing his authority.
• Pepin II of Aquitaine (son of the late Pepin I) → Excluded from the inheritance, fueling his discontent.

This arrangement favors Charles and Lothair, sidelining Louis the German and Pepin II, setting the stage for another civil war upon Louis the Pious’ death in 840.

The Death of Louis the Pious and the Civil War (840–843)

On June 20, 840, Louis the Pious dies, and almost immediately, Lothair I attempts to assert full imperial control, violating the agreements of Worms (839).

• On July 24, 840, in Strasbourg, Lothair declares his imperium over all Frankish lands, claiming overlordship over his brothers.
• He allies with his disinherited nephew, Pepin II of Aquitaine, and together they invade the Loire Valley, launching a campaign against Charles the Bald.

The Fracturing of the Empire: Divided Loyalties

The Carolingian nobility is divided in allegiance, particularly in Burgundy, where counts split between Charles and Lothair:

Lothair’s Supporters

• Ermenaud III of Auxerre
• Arnoul of Sens
• Audri of Autun
• Girard II, Count of Paris (Lothair’s brother-in-law)

Charles’ Supporters

• Guerin of Provence
• Aubert of Avallon

The War’s Outcome: The Treaty of Verdun (843)

The war continues until Charles the Bald and Louis the German defeat Lothair at the Battle of Fontenay (841) and solidify their alliance with the Oaths of Strasbourg (842). This culminates in the Treaty of Verdun (843), which permanently divides the Carolingian Empire into three distinct kingdoms:

• West Francia → Charles the Bald (precursor to France).
• Middle Francia → Lothair I, including the imperial title, but his kingdom will later fracture.
• East Francia → Louis the German (precursor to Germany).

Legacy of the 839 Partition and Civil War

• The dream of a unified Carolingian Empire collapses, marking the beginning of medieval Europe’s political map.
• The Frankish kingdoms begin evolving into separate entities, leading to the future emergence of France and Germany.
• Lothair’s imperial ambitions fail, and his Middle Frankish Kingdom proves unstable, setting the stage for further fragmentation.

Thus, the final partition of Louis the Pious in 839 directly leads to the division of Charlemagne’s empire, shaping the medieval European world for centuries to come.

Louis has rebuilt his political network by holding frequent assemblies of the lay and ecclesiastical nobility beginning in 835 and by presiding at ceremonies and ritual activities.

Hunting, his favorite pastime, has served him especially well in this regard.

He has also collected public revenue and directed successful military campaigns.

The emperor Theophilus in 839 had recognized Louis as his colleague and congratulated him on his stout defense of Christendom.

Louis, after reigning twenty-six years, dies at sixty-two on June 20, 840, at Petersau, a strongly fortified island in the Rhine River near Ingelheim.

He is buried in the monastery of Saint-Arnulf in Metz.

The civil war resumes.

Invasions of the Frankish empire by Vikings and Muslims have further weakened Carolingian power; the empire is now in serious decline.

Consort Wei had already died by the time her son took the throne, and Emperor Wuzong had posthumously honored her as an empress dowager.

Also, knowing that Yang Sifu and Li Jue had not supported him as Emperor Wenzong's successor, he had had them removed from their offices and instead installed Li Deyu, who was formerly a chancellor during Emperor Wenzong's reign, as a chancellor and effectively put most of the responsibilities of governance in Li Deyu's hands.

In 841, Emperor Wuzong further orders Liu Hongyi and Xue Jileng to commit suicide and plansto order Yang and Li Jue to do so as well, but Yang and Li Jue are spared (and only demoted) after the intercession of Li Deyu and the other chancellors Cui Gong, Cui Dan, and Chen Yixing.

Iconoclasm has been given full rein under Theophilos.

To weaken the political influence of Greek Orthodox monasticism, the Emperor and his former teacher John "the Grammarian", now patriarch of Constantinople as John VII, have mounted a persecution against the users of icons in Orthodox liturgy and devotion.

Support for Iconoclasm soon wanes, however, and the vast majority of the Greek Christians rally to the defense of their sacred art.

The cultural revival stimulated by Theophilos includes two significant advances in the area of classical studies: the gradual substitution of the minuscule, or smaller, cursive hand for the uncial, or larger, script, and the increase in the number of scriptoria, or copyists' workshops.

Theophilos has also restored the University of Constantinople after its eighth-century decline and appointed the brilliant teacher Leo the Mathematician as its new rector.

In the aftermath of the sack of Amorium, Theophilos had sought the aid of other powers against the Abbasid threat: embassies had been sent to both the western emperor Louis the Pious and to the court of Abd ar-Rahman II, Emir of Córdoba.

The imperial envoys had been received with honors, but no help has materialized.

The Abbasids, however, have not followed up on their success.

Warfare will continued between the two empires with raids and counter-raids for several years, but after a few imperial successes, a truce and prisoner exchange—which excludes the high-ranking captives from Amorium—is agreed in 841.