All around the world, immigration policies are unique from one country to the next. Each country has its own immigration policies that help protect its national interests. Some countries are much easier to immigrate to than others.
The strictest immigration policies in the world are policies for Vatican City, China and Japan.
To immigrate to Vatican City, you must be:
A Catholic Cardinal who is already living in Rome or Vatican City, or
A diplomat of the Holy See, or
A person whose job requires them to live in Vatican City
Some people are also able to become citizens by applying directly to the church administration, however, most people are not eligible for this method. To gain citizenship this way, you are required to be granted special permission to live in Vatican City, or you must be the child or spouse of someone who is a current resident.
China will only allow a foreign-born person to become a citizen of China if they permanently live in China, have relatives who are citizens of China, or if they have another reason to become a Chinese citizen. Very few people are able to qualify for citizenship given these requirements.
Anyone who wants to become a citizen of Japan must renounce their citizenship from other countries, live in Japan for five years, and undergo a tough interview and review process. Becoming a citizen of Japan can take years.
While there are many countries that have strict immigration policies, below are some other strict immigration policies of note.
This country issues residential permits via a lottery system. Anyone who would like to become a citizen must stay in the country for 30 years and must have permanent residents for five years before applying for citizenship. There is preference given to Swiss citizens. Anyone who becomes a citizen of Liechtensteinn must renounce their citizenship of other countries.
Bhutan only grants citizenship to people who are born of two Bhutanese citizens. If only one parent is Bhutanese, then the person must wait 15 years before becoming eligible for Bhutanese citizenship. People who do not have Bhutanese parents must live in Bhutan for 20 years before applying for citizenship. Government employees need only wait 15 years.