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Palestine is the most interesting country.
Zimbabwe
As an avid historian, I find almost any period interesting. If you live in the USA you will find that most people in that country like to study their own nation's history, with the Civil War period a clear front runner.
Here is an interesting, and well known, fact: China is the most populated country.
Its a country in Europe
Its a country in Europe
Not all the readers find the same character interesting. The most easily they can relate to a character, the more they find it interesting.
One interesting fact about the U.S. is although it is the youngest country around, it is the most powerful.
A lot of people found the ending interesting...
Personally, I find Brazil fascinating. Studying its wildlife is interesting. Another would be Saudi Arabia, looking at the politics there,
Your choice.
China is a country. Thus the an interesting country in China is... China!