Reign of Hong Taiji
Hong Taiji continued to expand the state in the region later known as Manchuria. He extended its power into Mongolia and raided both Korea and Ming China.
He also enlarged the Eight Banners, which became the means of integrating the peoples who joined the Manchus, above all Mongols and Han Chinese, whether after defeat or by agreement.
Mongolia and Korea
In the late 1620s and early 1630s Hong Taiji's armies and their Mongol allies defeated Ligdan Khan of the Chahar, the last Mongol ruler to claim the title of Great Khan. In 1635 Ligdan's son surrendered, reportedly handing over the imperial seal of the Yuan emperors, and Inner Mongolia came under Manchu control. Mongol Eight Banners were formed in the same year.
Korea was invaded twice. After the first invasion, in 1627, the Joseon court accepted terms but remained loyal to the Ming. When Joseon refused to acknowledge Hong Taiji as emperor, he invaded again in 1636. Early in 1637 the Korean king surrendered, broke off relations with the Ming and became a tributary of the Qing.
A New Name and a Chinese-Style State
In 1635 Hong Taiji decreed that his people should be called Manchu rather than Jurchen, and in 1636 he proclaimed himself emperor of the Great Qing. The new names helped to distance the state from the earlier Jurchen Jin dynasty, which the Han Chinese remembered as conquerors of the north.
Hong Taiji understood that a Manchu state ruling a large Han Chinese population would need Chinese officials. In 1631 he set up Six Boards on the Ming model, and he relied increasingly on Chinese advisers such as Fan Wencheng. Han Chinese banners were created alongside the Manchu and Mongol ones, growing to a full eight by 1642.
His armies kept up the pressure on the Ming. In 1641 and 1642 they won a decisive victory at Songshan and Jinzhou and captured the Ming commander Hong Chengchou, who went over to the Qing.