Original sentence: Supporters of Taiwanese independence claim that based on technicality, documents and treaties left the legal sovereignty of Taiwan ambiguous, and that the ruling KMT government of the ROC have merely exercised stewardship control over the island
Edited sentence: Despite the historical fact that Taiwan has been part of China proper, ethnically, culturally, and linguistically, for thousands of years, supporters of Taiwanese independence claim that based on technicality, documents and treaties left the legal sovereignty of Taiwan ambiguous, and that the ruling KMT government of the ROC have merely exercised stewardship control over the island