Fan Yang Mai, following years of internal trouble, overthrows the previous dynasty and seizes the Cham throne in 421.

Rugila, chieftain of the Huns, attacks the dioceses of Dacia and Thrace in the Balkans.

Theodosius II allows Pannonian Ostrogoths to settle in Thrace, to defend the Danube frontier.

Yazdegerd has tried to emancipate himself from the dominion of the magnates and of the Magi (a priestly caste serving a number of religions); thus, Christian and Zoroastrian sources view his reign differently.

Because he had stopped the persecution of the Christians, the Christian writers praise his clemency, but the sources dependent on Zoroastrian tradition refer to him as “Yazdegerd the Sinner.” He has also tried to limit the power of the nobles, but had finally answered their resistance with severity.

He has lived in peace and friendship with the Roman Empire and is therefore praised by Greek authors.

He appears to have been murdered in Khorasan, after which the nobles refuse to admit any of his sons to the throne.

However, one of them, Bahram, has the support of al-Mundhir, Lakhmid Arab king of Al-Hirah in Mesene (east of the lower Euphrates) and a Sassanian vassal, and also, apparently, of Mihr-Narseh, chief minister in Yazdegerd's last years, who is retained in office.

After Yazdegerd's death in 421, Persian nobles try to reclaim Bahram from Mundhir, so Mundhir sends his son Nu'man ahead with a brigade, then personally escorts Bahram with another brigade of 20,000 soldiers to Ctesiphon, where the nobles, after some negotiations, acknowledge Bahram as their ruler.

Bahram V, known as Gor (“the wild ass,” for his prowess in hunting the onager, reverses his father‘s policy of religious toleration, and revives the violent persecution of Christians in the Persian empire.

War breaks out between Constantinople and Ctesiphon because of the refusal of Theodosius to return to the Persians the Christians who have sought refuge from persecution in his empire.

In addition, the Persians have proven unwilling to return to the Romans gold-miners who had been working in Persian territory; they have also confiscated goods from Roman merchants.

Ardaburius, the emperor's magister militum praesentalis, conducts an invasion of Arzanene by way of Armenia.

After defeating the Persian commander Mihr-Narseh, …

…Ardaburius foils his opponent's attempt to ravage Mesopotamia, and besieges the Persians at Nisibis.

Bahram, in alliance with the Lakhmid Arabs of Hirah, marches with al-Mundhir to lift the siege.

Honorius appoints as coemperor the patrician Flavius Constantius, husband to the emperor's half sister Galla Placidia, on February 8, 421, but Constantius III, as he is known, dies suddenly within the year, without having been recognized by the eastern emperor, Theodosius II.

Galla Placidia, widowed a second time, departs with her children Grata Honoria and Valentinian to the court of Constantinople.

(Her son, as Valentinian III, will succeed Honorius as emperor of the West from 425 to 455.)

The Franks conquer new territories in their kingdom and sack the old Roman capital Augusta Treverorum (modern Trier).

Emperor Mingyuan's wife Consort Yao had died in 420, and he posthumously honored her as an empress.

The Emperor suffers a major illness in 422, apparently caused by medicines that alchemists had given him that were supposedly capable of extending life spans.

He consults Cui Hao on what he should do to prepare for events after his death.

Cui Hao predicts that he will recover, but advises him to create his oldest son, fourteen-year-old Tuoba Tao, the Prince of Taiping, crown prince, then transfer some of the authorities to the crown prince so that his own burdens could be lessened.

Baba Song also agrees, and Emperor Mingyuan creates Tuoba Tao crown prince, and further has Crown Prince Tao take the throne to serve as the secondary emperor.

He commissions his key advisors Baba, Cui, Daxi Jin, Anchi Tong, Qiumuling Guan, and Qiudun Dui to serve as the Crown Prince's advisor.

From this point, Crown Prince Ta rules on most matters, particularly domestic matters, while Emperor Mingyuan himself only rules on important matters.

Later in 422, after hearing about the death of Liu Yu (who had seized the Jin throne in 420 and established Liu Song), Emperor Mingyuan breaks off relations with Liu Song and calls his council, informing the advisors that he plans to attack and seize three major cities south of the Yellow River from Liu Song—Luoyang, Hulao, and Huatai, despite Cui's opposition.

He commissions Daxi as the commander of the forced to attack Liu Song.

Daxi first puts Huatai under siege, but after he is unable to capture it quickly, Emperor Mingyuan personally led an army south to aid Daxi.

He also has Crown Prince Tao lead an army to the northern border, to guard against a Rouran attack.

Huatai then falls.

Daxi now approaches Hulao and Luoyang.

Meanwhile, Emperor Mingyuan also sends the generals E Qing, Lü Dafei, Pu Ji, and Yizhan Jian east, capturing several prefectures in modern western Shandong.

However, while other cities in Song's Qing Province (modern central and eastern Shandong) fall as well, the Northern Wei forces are unable to capture the capital of Qing Province, Dongyang (in modern Qingzhou, Shandong), and are eventually forced to withdraw after food supplies run out and a large number of soldiers grow ill.