Question: [The Wikipedia article on Korea](https://en.wikipedia.org/wiki/Korea) states that South Koreans call Korea 한국, while north Koreans call it 조선. Do 'Korea', '한국', and '조선' all refer to the same thing? If so, how did the three different names come about?

Answer: 
Basically, 'Chosun' is the old name of 'Korea'. Used a lot in the past, it is rarely used anymore. 'North Korea' still uses the term 'Chosun', but it is rarely used in South Korea. That's why you have to understand the two words differently.
'Joseon(조선)' is a country that has been destroyed and does not exist at present. In a modern society divided into South and North Korea(북한), there is only North Korea that calls itself Joseon. The official name of Korea (남한, South Korea) is Republic of Korea.