Prior to Koxinga, it was an island that Fujian people escaping the grip of imperial tyranny went to.  Koxinga's dad used it as a base to fight the imperial forces.  Koxinga used it as a base to fight against the Machurian control over China for the Southern Han.  Since then, Taiwan has been a preserver of Han culture.  It is still a preserver of Han culture when the Cultural Revolution wiped out most of the Chinese culture,

Sure, corrupt KMT caused plenty of suffering in China and was part of the reason why the CCP rose to power.  KMT's escape to Taiwan was part of a trend that went back centuries.  

Taiwan always have foreign intervention, starting from the Portuguese, Dutch, Spanish, Japanese and now the Americans.  

China has to accept the unique circumstance of the existence of Taiwan and work with the island as a co-partner of Chinese civilization instead of a big brother small brother perspective.   The CCP may be able to power its way to control Taiwan, with history as a guide, the cost will be too high.