In 1592, Toyotomi Hideyoshi of Japan sent a large army to conquer Korea, and in just one month, Korea was on the verge of collapse by "three capitals lost and eight roads collapsed". Later, with the assistance of the Ming Dynasty army, after several years of war, Japan was finally expelled from the Korean Peninsula! It is reasonable to say that the DPRK had the grace to restore the country to Korea, but more than ten years later, in the early days of the war between the Ming Dynasty and the Later Jin Dynasty, the Lee Dynasty of Korea was at both ends.
First, diplomatic tug-of-war
In 1618, Nurhaci provoked war against the Ming Dynasty and led troops to capture Fushun, Qinghe and other places. When the war report reached Beijing, the Ming court decided to attack Nurhaci in a big way, so it appointed Yang Hao as the Economic Strategist of Liaodong and recruited troops from all over the country. At the same time, the official documents of the Ming Dynasty's troop transfer were also issued to the DPRK, allowing them to send tens of thousands of troops and take the lead alone. At that time, the king who ruled Korea was Lee Hun, the king of Gwanghaejun, who was reluctant to send troops from beginning to end.
Guang Haijun believed, "What is the benefit of our country's three-sided defense and self-defense, and what is the benefit of taking a weak pawn and not teaching, and entering the Heavenly Dynasty?" At the same time, he also felt that "the old chieftain, although he used the strength of the Chinese and North Korean troops, could not be eliminated in one fell swoop." To this end, north Korea and the Ming Dynasty launched a period of diplomatic tug-of-war, and finally "the arm could not twist the thigh", and the DPRK was forced to agree to send troops to help. However, after some haggling, the Ming agreed that The North Koreans would reduce the number of troops sent and let them cooperate with the Ming army.
2. The Battle of Salhu
On February 29, 1619, the Ming Dynasty's hundreds of thousands of troops, divided into four routes, launched an attack on Houjin. The Korean Kwanghaejun sent 15,000 men, led by Marshal Kang Hongli, a North Korean force under the control of Liu Kai, the main commander of the Ming Southern Route Army. After the battle, Nurhaci adopted various tactics of breaking, concentrating superior forces to first annihilate Juniper's Western Route Army, and then defeat the Northern Route Army led by Marin. After that, Nurhaci led the main force to deal with Liu Que of the Southern Route Army.
In the Battle of Abdaligang, Liu Que fell into the encirclement of Houjin and died in battle, almost completely destroying the army. The North Korean army led by Kang Hongli barely fought much, and all of them raised their hands and surrendered. What is even more surprising is that before the Battle of Salhu, Guang Haijun had actually revealed to the merchants of Houjin that he was going to send an army to follow the Ming Dynasty, "Our country was forced by the Chinese and Korean Dynasties to send troops, and when it was after the Tang Dynasty, it must be aware."
Third, Guang Haijun's choice
After Jiang Hongli surrendered, he handed over all the Ming soldiers who fled to the Korean army to Houjin, and they also wanted to sacrifice the Ming guerrilla Qiao Yiqi to Houjin, who committed suicide in anger after hearing the news. So why did Guang Haijun pursue this diplomatic strategy of two ends of the rat? There are two main reasons: First, Guang Haijun had a feud with the Ming Dynasty. Gwanghae-jun was the second son of Hyunjo of Joseon, and he had an elder brother above him, so his status as a son of the ming dynasty has never been recognized by the Ming Dynasty.
In 1608, Joseon Seonjo died of illness and was succeeded by Gwanghae-jun, but the Ming Dynasty still refused to admit it, and even sent people to investigate. Guang Haijun took out tens of thousands of taels of silver to bribe Ming officials to open the joints, and finally arrived at the ming dynasty's canonization in the following year. Because of this incident, Guang Haijun always held a grudge against the Ming Dynasty. Second, realistic interests. The North Korean side was very clear about the strength of the Ming Dynasty and the Later Jin Dynasty, so Guang Haijun believed that it would be difficult for the Ming Dynasty to win this battle. For the sake of his own national interests, he adopted a strategy of two ends of the head, neither offending the Ming Dynasty nor the Later Jin.
References: 1. "History of Ming"; 2. "Diary of Guanghai Jun"; 3. "Records of Manchuria"