United Nations

What are two countries that are not apart of the United Nations and why do they refuse to join? I found that Taiwan used to be part of the United Nations, but after the year of 1971 they were replaced by China. It is interesting that still to this day Taiwan is not considered independent, although it meets the requirements. This is mainly because of political reasons. Whereas Kosovo it a country who took it upon themselves to be an independent country, which has the right to observe the United Nations. Apparently there is a specific number of criteria that must be passed in order to meet the requirements to join the United Nation and Kosovo is one of those countries that meet the criteria.