Original:  It  was founded by Koxinga (Zheng Chenggong) as part of the loyalist movement to restore the Ming dynasty on the Chinese mainland after its rump state in  southern China was overthrown by the Manchu-led Qing dynasty.
Revised:  It was founded by Koxinga (Zheng Chenggong) as part of the loyalist movement to restore the Ming dynasty on the Chinese mainland , when the Ming remnants' rump state in southern China was overthrown by the Manchu-led Qing dynasty.
Edit intent: clarity