<P> The unbroken series of military successes by Nurhaci came to an end in January 1626 when he was defeated by Yuan Chonghuan while laying siege to Ningyuan . He died a few months later and was succeeded by his eighth son, Hong Taiji, who emerged after a short political struggle amongst other potential contenders as the new Khan . </P> <P> Although Hong Taiji was an experienced leader and the commander of two Banners at the time of his succession, his reign did not start well on the military front . The Jurchens suffered yet another defeat in 1627 at the hands of Yuan Chonghuan . As before, this defeat was, in part, due to the Ming's newly acquired Portuguese cannons . </P> <P> To redress the technological and numerical disparity, Hong Taiji in 1634 created his own artillery corps, the ujen cooha (Chinese: 重 軍) from among his existing Han troops who cast their own cannons in the European design with the help of defector Chinese metallurgists . One of the defining events of Hong Taiji's reign was the official adoption of the name "Manchu" for the united Jurchen people in November 1635 . In 1635, the Manchus' Mongol allies were fully incorporated into a separate Banner hierarchy under direct Manchu command . Hong Taiji conquered the territory north of Shanhai Pass by Ming Dynasty and Ligdan Khan in Inner Mongolia . In April 1636, Mongol nobility of Inner Mongolia, Manchu nobility and the Han mandarin held the Kurultai in Shenyang, recommended khan of Later Jin to be the emperor of Great Qing empire . One of the Yuan Dynasty's jade seal has also dedicated to the emperor (Qing Taizong) by nobility . When he was said to be presented with the imperial seal of the Yuan dynasty after the defeat of the last Khagan of the Mongols, Hong Taiji renamed his state from "Great Jin" to "Great Qing" and elevated his position from Khan to Emperor, suggesting imperial ambitions beyond unifying the Manchu territories . Hong Taiji then proceeded in 1636 to invade Korea again . </P> <P> After the Second Manchu invasion of Korea, Joseon Korea was forced to give several of their royal princesses as concubines to the Qing Manchu regent Prince Dorgon . In 1650, Dorgon married the Korean Princess Uisun . </P>

6 reasons why the qing empire declined in china