The next few years of the reign witnessed the return of many captives taken by the Japanese during the years of the invasion; they beheld the promulgation of the law that no one could marry during the three years of mourning for a parent; also a scourge of cholera so terrible as to cause the king to send and sacrifice upon the eight high mountains of Korea. A powerful conspiracy, led by the prime minister, Sim Keui-wŭn, came near overthrowing the dynasty, but the alarm was given in the very nick of time and he and his fellow conspirators were seized and executed.
The twenty-first year of the reign, 1643, beheld the fall of the Ming dynasty in China. The pretext given by the Manchus for marching on Nanking was the revolt of Yi Cha-sung who burned Nanking and drove the emperor to suicide. Then, terrified at his own deed, he fled and the Manchus stepped in. When Nanking fell, a letter was despatched to Korea saying “I am the greatest of rulers. You have long been my vassal and I will now show you a favor by returning your hostage, the Crown Prince.”
A word is necessary as to the fate of Im Kyöng-ŭp, one of the men who had been sent to Manchuria with Ch‘oé Myŭng-gil. He succeeded in making his escape before the party reached the Yalu and in the disguise of a monk made his way in a merchant boat to Teung-nă where he attached himself to Gen. Whang Chong-ye and made himself very useful. It is said that he made himself famous by capturing a notorious pirate. He sailed straight for the island on which the pirate had his headquarters and having gotten the pirate and his crew drunk with wine he bound and brought them safely to the Chinese camp. Later he fell into the hands of the Manchus through treachery but was so steadfast in his refusal to do obeisance to them that he excited their unbounded admiration, and they let him go back to Korea. This was an unfortunate move for him, for in the meantime Kim Cha-jŭm had been recalled from banishment and had become court favorite. As these men were deadly enemies the returning general was immediately seized and put to death. This same year saw the publication of the historical work named the Tong-sa Po-byŭn.
In the following year the Crown Prince and his brother returned from China but the Crown Prince soon after sickened and died. It had been customary heretofore for the king and queen to assume mourning for three years for a Crown Prince but now an innovation was made and thirteen months was the limit set. Of course the succession fell to the infant son of the dead prince, but, the wife of prince Pong-im, the second son of the king, was extremely ambitious to become queen, and so she went about to gain the desired end. By every means in her power she brought pressure to bear upon the king to induce him to set aside the infant prince and nominate her husband as heir to the throne. She was partially successful and the following year the king called his courtiers together and consulted as to the advisability of the plan. He urged that the real heir was but a babe in arms and that he himself was old and about to go the way of all the earth. It was evident that he desired to put Prince Pong-im on the throne, and a very animated discussion followed. Most of the leading ministers and officials argued against the plan saying that it was contrary to the best traditions of the land and that the people all looked to the young prince as their future ruler. To all these arguments the king opposed counter arguments which revealed plainly that he had already made up his mind as to his course, and that he was merely seeking for confirmation of his views. Kim Nyu then said, “If the king has already made up his mind let him speak out and put an end to this useless discussion.” The king then announced that Prince Pong-im was to be his successor.