In the mid-17th century, most of China has been conquered by the Manchu-led Qing dynasty after the collapse of the Ming dynasty. Ming remnants have fled south and established a Southern Ming regime based in Fujian Province, with the Longwu Emperor as their figurehead monarch. The Qing armies are closing in on Fujian and the southern areas under Ming control.
Zheng Sen is the son of Zheng Zhilong, a former pirate who became a Ming general. Having heard of Zheng Sen's strong sense of loyalty, the Longwu Emperor is so impressed with him that he grants him the imperial family name, Zhu, and a new personal name, Chenggong (literally "success"). Zheng Sen is known as the Imperial Name-keeper (transliterated "Koxinga") or Zheng Chenggong from then on. Around the time, Taiwan has been colonised by the Dutch East India Company for over three decades and many people have signed a petition requesting Zheng Chenggong to help them claim back Taiwan from the Dutch.
Zheng Zhilong defects to the Qing dynasty after seeing that he has no future in Southern Ming. Despite his father's betrayal, Zheng Chenggong remains loyal to the Longwu Emperor and continues to resist the Qing invaders even after the fall of Southern Ming. He plans to retreat to Taiwan and establish a new base of operations there in preparation for retaking Mainland China from the Qing dynasty.
In 1661, Zheng Chenggong's fleet sets sail from Xiamen to attack the Dutch on Taiwan. Nine months later, he defeats the Dutch at the Siege of Fort Zeelandia and forces them to surrender and relinquish their control of Taiwan to him.
