Taiwan

D: A small, but successful sovereign island off the coast of China.

Taiwan is a sovereign region by virtue of the fact that it is controlled by a local government, and not one based in mainland China.

Over the past 105 years, Taiwan has been controlled by mainland China for approximately five of them. In spite of this low number, the Chinese government are insistent that Taiwan is part of China, and must be brought under control of Beijing. Few mainland Chinese actually know about this 5/105 year ratio - but they all know that Taiwan must be part of China because they have been told this enough for them to believe it, and 6453 repetitions make a truth.

The reason for this apparent lack of rationality by the Chinese dictatorship is because Taiwan is the proof of their own failures. In 1948, Taiwan and China were very similar.

Both populations were the same race.
Both populations had similar history.
Both populations had an almost identical culture.
Both regions had almost the same level of wealth, education and development.

In just 50 years, Taiwan has become a relatively free, educated and successful democracy, whereas China is a corrupt dictatorship whose people live without personal freedom or personal wealth. It is (apart from North Korea and South Korea) the most poignant illustration of the failure of communism.

Those who object to this argument typically suggest that

Taiwan was subsidized by the US. Anyone who thinks that the US selling them cheap weapons which have never been used has helped their economy needs a lesson in basic mathematics.
Taiwan took all the gold with them when Chiang Kai Shek fled the mainland. Anyone who thinks that a few tonnes of useless yellow metal sitting idly in a locked room for the last 50 years could account for the difference needs a basic lesson in economics. It may have provided a small amount of stabilization for their currency, but that is all.

Most mainland Chinese say they are prepared to go to war for an extended period to 're-take' Taiwan. The losses would be so high if this were to happen, that the Chinese dictatorship would not survive. Unfortunately unstable dictatorships sometimes do stupid things to try to prop up their power-bases. It is in everyone's interest for the Chinese dictatorship to be dismantled slowly.

See