Noorhachu was succeeded by his fourth son, the fourth Beira or Prince, known as Taitsong, who continued both his work and policy. Taitsong was as determined to humiliate the Mings as his father had been. He commenced his offensive measures by an attack on Corea, which he speedily reduced to such a pass that it accepted his authority and transferred its allegiance from the Mings to the Manchus. This was an important success, as it secured his eastern flank and deprived the Chinese of a useful ally in the Forbidden Kingdom. It encouraged Taitsong to think that the time was once more ripe for attacking Ningyuen, and he laid siege to that fortress at the head of a large army, including the flower of his troops. Notwithstanding the energy of his attack, Chungwan, the former bold defender of the place, had again the satisfaction of seeing the Manchus repulsed, and compelled to admit that the ramparts of Ningyuen presented a serious if not insuperable obstacle to their progress. Almost at the very moment of this success the Emperor Tienki died, and was succeeded, in 1627, by his younger brother, Tsongching, who was destined to be the last of the Ming rulers.
The repulse of Taitsong before Ningyuen might have been fatal if he had not been a man of great ability and resource. The occasion called for some special effort, and Taitsong proved himself equal to it by a stroke of genius that showed he was the worthy inheritor of the mission of Noorhachu. Without taking anybody into his confidence he ordered his army and his allies, the Kortsin Mongols, to assemble in the country west of Ningyuen, and when he had thus collected over a hundred thousand men, he announced his intention of ignoring Ningyuen and marching direct on Pekin. At this juncture Taitsong divided his army into eight banners, which still remain the national divisions of the Manchu race. The Manchus seem to have been a little alarmed by the boldness of Taitsong's scheme, and they might have hesitated to follow him if he had given them any time for reflection, but his plans were not fully known until his forces were through the Dangan Pass on the march to the capital. The Chinese, relying altogether on Ningyuen as a defense, had made no preparation to hold their ground on this side, and Taitsong encountered no opposition until he reached Kichow. Then Chungwan, realizing that he had been outmaneuvered, and that the defenses of Ningyuen had been turned, hastened back by forced marches to defend Pekin. Owing to his road being the better of the two he gained the capital in time, and succeeded in throwing himself and his troops into it in order to defend it against the assault of the Manchus. After Taitsong sat down before Pekin he engaged in an intrigue for the ruin of Chungwan, whose disgrace would be equivalent to a great victory. The method is not to be approved on general grounds, but Taitsong conceived that he was justified in bribing persons in Pekin to discredit Chungwan and compass his ruin. The emperor was persuaded that Chungwan was too powerful a subject to be absolutely loyal, and it was asserted that he was in communication with the enemy. Chungwan, who had been so long the buttress of the kingdom, was secretly arrested and thrown into a prison from which he never issued. The disappearance of Chungwan was as valuable to Taitsong as a great victory, and he made his final preparations for assaulting Pekin; but either the want of supplies or the occurrence of some disturbance in his rear prevented the execution of his plan. He drew off his forces and retired behind the Great Wall at the very moment when Pekin seemed at his mercy.
During four years of more or less tranquillity Taitsong confined his attention to political designs, and to training a corps of artillery, and then he resumed his main project of the conquest of China. Instead of availing themselves of the lull thus afforded to improve their position, the Chinese ministers seemed to believe that the danger from the Manchus had passed away, and they treated all the communications from Taitsong with imprudent and unnecessary disdain. Their attention was also distracted by many internal troubles, produced by their own folly, as well as by the perils of the time.
Taitsong, in 1634, resumed his operations in China, and on this occasion he invaded the province of Shansi, at the head of an army composed largely of Mongols as well as of Manchus. Although the people of Shansi had not had any practical experience of Manchu prowess, and notwithstanding that their frontier was exceedingly strong by nature, Taitsong met with little or no resistance from either the local garrisons or the people themselves. One Chinese governor, it is said, ventured to publish a boastful report of an imaginary victory over the Manchus, and to send a copy of it to Pekin. Taitsong, however, intercepted the letter, and at once sent the officer a challenge, matching 1,000 of his men against 10,000 of the Chinese. That the offer was not accepted is the best proof of the superiority of the Manchu army.