Below are 8 (eight) countries where it is most difficult to become a citizen:
1-Vatican City State
You can become a citizen of this country if you are a Cardinal currently residing in the Vatican or Rome, or if you live in the Vatican because you are an employee of the Catholic Church.
2-Bhutan
You can apply for citizenship after living in this country for 20 years and you must fulfill the requirements including no history of speech or actions that oppose/resist the king and the state.
3-Qatar
If you have been a legal resident of Qatar for 25 years without leaving the country for more than two consecutive years, you can become a citizen. Qatar only naturalizes about 50 foreigners each year.
4-Kuwait
After living in Kuwait for 20 years, or 20 years for residents of non-Arab countries, you can apply for Kuwaiti citizenship. However, you must be a Muslim by birth or convert to Islam. If you convert to Islam, you must have practiced it for five years and be able to speak Arabic fluently.
5- Liechtenstein
If you want to become a citizen of Liechtenstein, you must have lived in Liechtenstein for at least 30 years or if you are married to a citizen of Liechtenstein and have already lived in this country, then the period can be shortened to 5 (five) years from the date of marriage.
6- United Arab Emirates (UAE)