When the Republic of China was first established it had the entire mainland China plus the island of Taiwan under its belt. In 1945, a communist government called the People's Republic of China attempts to take over China. As the fight goes on, the Republic of China is pushed back to the Island of Taiwan, where is still resides today. The area where the Republic of China started in was not colonized at any point, and this republic still claims mainland China, while the People's Republic claims the island of Taiwan.
You need to go back further. Prior to that, Taiwan was partly colonized by the Dutch and Spanish, and then given to the Japanese. You can read all about it on Wikipedia's page on the history of Taiwan.
Who were Spain and France colonized by? If we're going way back before the countries formed, the U.K. (England) was conquered and reformed several times.