"Ma said under the ROC Constitution, the ROC “definitely is an independent sovereign state, and mainland [sic] China is also part of the territory of the ROC.”

The interview was published yesterday.

Ma said despite the stipulation of the ROC Constitution, Taiwan cannot recognize the existence of another country, nor does China want to recognize Taiwan. In other words, under the ROC Constitution, “mainland China” is not a country."

from http://www.taipeitimes.com/News/taiwan/archives/2008/10/08/2...

via https://en.wikipedia.org/wiki/One-China_policy

Ma Ying Jeou and the KMT have some persuasive arguments; there was an interview on YouTube where he eloquently explained why these claims exist; the mainland Chinese Communist party came to power without being elected by the people. Also, when Japan signed its surrender papers giving up its claims to annexed territories, the sovereignty reverted to the KMT government.