Heraclius prepares to leave Constantinople and moves…

Wang Shichong at Luoyang has Yang Tong yield the throne to him in spring 619, ending the Sui dynasty and establishing a new state of Zheng.

Around the same time, Li Gui, while stating that he wishes to be a Tang subject, refuses the Tang creation of Prince of Liang, instead declaring himself the Emperor of Tang.

In summer 619, Li Gui's official An Xinggu, formerly a Tang official, rebels against Li Gui and captures him, submitting to Tang.

Gaozu executes Li Gui and incorporates his domain into Tang.

Also around the same time, …

…Li Mi, having been defeated earlier in the year in a surprise attack by the Sui general Wang Shichong, flees to Tang territory and submits to Gaozu.

Li Mi's general Xu Shiji, who controls a major part of Li Mi's former territory, also submits, and Emperor Gaozu, impressed with Xu's faithfulness to Li Mi, bestows the imperial surname of Li on Xu.

Gaozu creates Li Mi the Duke of Xing, but only makes him the Minister of Feasts, a post that Li Mi views as below his stature.

Around New Year 619, Li Mi requests Emperor Gaozu's permission to head east to persuade some of his former subordinates to submit to Tang, but once he leaves Chang'an, plans to restore his independence.

He is ambushed and killed by the Tang general Sheng Yanshi.

…the rebel leader Du Fuwei, who controls the modern southern Anhui, submits to Tang, and Gaozu also bestows the imperial surname of Li on him, creating him the Prince of Wu.

Similarly, …

…Luo Yi, who controls the modern Beijing region, submits, is bestowed the imperial surname of Li, and is created the Prince of Yan.

The Persian forces in Egypt, after defeating the imperial garrisons in the Nile Valley, march across the Libyan Desert as far as Cyrene.

Tang is meanwhile facing another serious threat—Liu Wuzhou, now determined to march south against Tang.

Emperor Gaozu sends Pei Ji against Liu's advancing army, but Pei is defeated by Liu, who then puts Taiyuan under siege.

Li Yuanji flees back to Chang'an, and much of modern Shanxi is seized by Liu.

Emperor Gaozu then sends Li Shimin against Liu, and by summer 620, Li Shimin has defeated Liu, forcing him to flee to the Eastern Turks.

Liu's territory is incorporated into Tang.

Around the same time, however, Dou Jiande the Prince of Xia makes a major offensive against the cities that had submitted to Tang in modern Hebei and Henan, north of the Yellow River, seizing nearly all of them and taking captive Emperor Gaozu's cousin Li Shentong the Prince of Huai'an, Emperor Gaozu's sister the Princess Tong'an, and Li Shiji's father Li Gai.

With Li Gai in Dou's custody, Li Shiji surrenders to Dou as well.

In 620, Li Shiji, in association with another Tang general who had surrendered to Dou, Li Shanghu, plots to ambush Dou, but the plot is discovered; Li Shanghu is killed, and Li Shiji flees back to Tang.

Li Fuwei, in 620, captures much of the lower Yangtze River territory of another agrarian ruler, Li Zitong, the Emperor of Wu, in the name of the Tang Dynasty.

Li Zitong, in turn, defeats and takes over the territory of Shen Faxing the Prince of Liang, roughly modern Zhejiang.

Emperor Gaozu, delegating control of his military and civil administration in the east to Li Shimin, concentrates on reforming coinage and taxation.

Weltenburg Abbey, founded by Irish or Scottish Benedictine monks in about 620 and held to be the oldest monastery in Bavaria, is situated on a peninsula in the Danube, on the so-called "Weltenburg Narrows" or the "Danube Gorge".

The Persians have pushed the imperial forces back to Constantinople by 620.

The great days of the Persian Achaemenid Empire seem to have come again, and there is little in the recent history of Constantinople's emperors that encourages Heraclius to place much faith in the future.

He clearly cannot hope to survive unless he keeps under arms the troops he has brought with him; yet, the fate of Maurice demonstrates that this will be no easy task, given the empire's lack of financial and agricultural resources.

He now begins a campaign against Persia to retake the territories conquered by Khosrau.