 The ROC proclaimed Taiwan Retrocession Day on October 25, 1945.However, due to the unresolved Chinese Civil War, neither the newly established People's Republic of China (PRC) in mainland China nor the Nationalist ROC that retreated to Taiwan was invited to sign the Treaty of San Francisco, as neither had shown full and complete legal capacity to enter into an international legally binding agreement.Since China was not present, the Japanese only formally renounced the territorial sovereignty of Taiwan and Penghu islands without specifying to which country Japan relinquished the sovereignty, and the treaty was signed in 1951 and came into force in 1952.