In late 1643, Hong Taiji who had been preparing to renew the war against Ming, suddenly died. There was an immediate power struggle as a result between the two likeliest successors Hooge (Hong Taiji's son) and Dorgon (Hong Taiji's younger brother) that lasted two years. Both were capable military leaders and had the support of some Banners. The fighting ended when they compromised by placing Fulin (son of Hong Taiji but a child emperor) on the throne. However the power struggles would not end there, but for the time being Dorgon had the upper hand and so he implemented a radical new strategy for defeating the previously invincible bastion forts.
From 1645 when the war resumed under Dorgon, the lines were essentially stalemated with both sides mastering the construction techniques for building the bastion fort. Despite studying the design and learning how to build them themselves, the Manchu had not found any weakness or vulnerabilities that they could exploit. It seemed like the ultimate design in fortifications building against gunpowder weapons at least, and the only possible method of taking it, was to storm it with force, and accept horrendous casualties in doing so. Therefore the Dorgon decided on a new policy of using captured Korean prisoners of war to force Ming garrisons to expend gunpowder and ammunition on them, before attacking in strength with their main army. This strategy was successful to a certain extent, but it still resulted in horrendous losses for the Manchu, and running out of Korean captives, they soon began using Han settlers that they could find and capture. A dozen bastion forts were captured by the Manchu in this way.
This however had the cost of outraging the previously supportive Han population in Liaodong who turned against the Manchu. Subsequently the Manchu saw the desertion of some capable Han commanders and their soldiers who defected back to the Ming including both Kong Youde and Geng Zhongming who had originally mutinied against Sun Yuanhua. Chongzhen by this time was offering actual rewards to Han commanders who deserted the Manchu if they could bring troops with them as well. Both Kong Youde and Geng Zhongming were pardoned by the emperor, rewarded, and then dispatched to far-off Yunnan to fight with barbarians there as the emperor obviously did not trust them to fight the Manchu.
With their enemy weakened, Ming forces led by Wu Sangui decided to march on the Manchu and met them in open battle near Jinzhou. In this battle they revealed a new technology for the first time. By 1645, Ming had developed canister shot, brought by the Jesuits from Europe, which was brutally effective not only against infantry, but also cavalry if fired en masse. Thus in the battle of Jinzhou, Manchu's traditional advantage in cavalry was all but negated.
With Dorgon’s defeat, Hooge saw an opportunity to challenge him again and so the Manchu banners were again split in civil war. This gave the opportunity for various Mongol princes to renege their loyalty to the Manchus (helped by Ming bribes). Joseon Korea also withdrew their support although they stopped short of supporting Ming. The ensuing civil war massively weakened the Manchu before Hooge was defeated in 1651. But this was not the end of their troubles, because Fulin then attempted to depose his uncle and claim the reins of power for himself, and Dorgon imprisoned the Manchu emperor creating much dissent among the banners.
Ming was not free from political instability either. Just as the danger from internal rebellions seemed to be receding in 1644, there was an attempted coup by eunuchs to poison the emperor and replace him with his 15 year old son that they hoped to better control. The eunuchs had long been dissatisfied with the growing power of the Confucian bureaucrats favoured by Chongzhen, but they were much more angry with the flood of new Jesuits pouring into China and turning their emperor agains them. The coup was an unmitigated disaster for the eunuchs who were not as unified as they thought, for the emperor had placed many informers within their ranks for obvious reasons. The coup would see a purging of their ranks, thousands executed, their subsequent exclusion from all top political posts, and the emperor giving his firstborn son and heir to Confucian officials but also the Jesuits for education rather than trusting his eunuchs. The son, Zhu Cilang was found wholly innocent of any knowledge of the plot as the eunuchs had not involved him.
Around this time, Ming had also begun to recover economically as the provinces had several successful harvests in a row, the negative impact of the spike in the value of silver had passed, and as people began to get used to a reduced silver flow, they were willing to circulate silver again. In addition, flooding in the Yangtze and Yellow rivers had been contained and the series of plagues that afflicted the empire were beginning to die down.
In addition a new generation of talented commanders had come to the fore which included Wu Sangui, Zu Dashou, as well as older ones who continued to serve with distinction such as Hong Chenchou and Sun Chuanting. Hong Chengchou had effectively stamped out all internal rebellions over the past few years. Wu Sangui and Sun Chuanting led the offensive against the Manchus who were now in disarray, but Ming progress was slow as besieging the bastion forts took a long time. Zu Dashou meanwhile negotiated successfully with the Khorchin and Chahar by leading an expedition over the Great Wall, the first for Ming in many years, which persuaded the local tribes to make peace with Ming.
Another headache for the Manchu came when Russian representatives arrived at the Forbidden City for an audience with the emperor. The Russians had prostrated themselves in front of the emperor performing the required tribute of nine kowtows in rather clumsy fashion before getting to their feet unsteadily. Arriving at the Amur river basin only in the past year, they had reached Beijing via Joseon Korea and crossing into China from Liaodong. The emperor agreed with an alliance with their far-off Tsar on the condition that he supply thousands of men to attack and put pressure on the Manchu from the northeast. Ming also agreed to supply the Russians with some cannon and attack to try to recover all of Liaodong at the same time.
This Russian-Ming alliance was a nuisance for the Manchu who now faced enemies on two fronts not to mention the desertion of most of their Mongol allies. Had they faced the Russians alone, it would be quite simple to defeat them, but they had to contend with 200,000+ Ming troops in Liaodong all equipped with new and capable cannon able to use canister shot. As representative of the Ming court to the Russians, Chongzhen decided to appoint Li Zicheng, an officer recommended by Wu Sangui. After all the burly Russians and the rustic officer that escorted them to Beijing seemed to get along together.
Li Zicheng had started out as a bandit in Shaanxi, second in command only to Dao Yingxiang (who had been nicknamed the Dashing King). But after their defeat to Yuan Chonghuan, he had been captured by Ming forces and exiled to Liaodong where he worked as a labourer for the next ten years building fortifications, as punishment for banditry. After this, he had joined the army again in Liaodong and was accepted due to his prior experience. Rising rapidly through the ranks, he became an officer and soon struck up a friendship with General Wu Sangui who at that time had just been promoted by the emperor as governor of Liaodong. Wu promoted Li and he had been commander of a battalion of 1000 troops guarding a star fort fighting the Jurchens when a band of foreigners had approached. Finding translators had been immensely difficult, but fortuitously one captured Jurchen/Manchu had known the language, and Li had been appointed by Wu Sangui to escort the Russians to Beijing.
