Historically speaking, "Chosŏn" (also romanized as "Joseon") referred to the northern area and "Han" (한; 韓) to the southern region in general. Until about 2000-3000 years ago, several ancient kingdoms in northern Korea had the name "Joseon," including Go-Joseon, Wiman Joseon, and Gija Joseon, while several tribes in southern Korea -- collectively called the "Three Han" (Samhan; 삼한; 三韓) -- used the name "Han."
By the beginnning of the Common Era, northern Korea was controlled by the kingdom of Goguryeo (고구려; 高句麗). Soon after, the three southern Han tribal confederacies resolved into the kingdoms of Baekje (백제; 白濟), Silla (신라; 新羅), and the minor kingdom of Gaya (Garak). Several centuries after the fall of the Baekje's and Goguryeo's fall to Silla and Silla's subsequent fall to Goryeo, the Samguk Sagi ("History of the Three Kingdoms") was written, which gave the collective name "Three Kingdoms" (Samguk; 삼국; 三國) to Goguryeo, Baekje, and Silla.
Baekje and Goguryeo came under Silla's control in the 660s, making Silla the first kingdom to rule the entire peninsula. Thus, Korea's name became "Silla." The country is often referred to today by historians as "Unified Silla" (Tongil Silla; 통일 신라; 統一新羅) to differentiate it from the Silla of the Three Kingdoms Period.
In the 930s, the new kingdom of Goryeo (고려; 高麗) conquered Silla. The name "Goryeo" (a shortened form of "Goguryeo") was translated into Italian as "Cauli," the name Marco Polo used when mentioning the country in his Travels. From "Cauli" came the English names "Corea" and the now more commonly used "Korea" (see Western names below).
After Yi Seonggye founded the Joseon Dynasty in 1392, he renamed the country "Joseon," reviving the old name. The country's full name was Daejoseonguk (대조선국; 大朝鮮國; "Great Joseon Nation"), a name that is almost never used today. In 1897, King Gojong became the first emperor of the newly formed Korean Empire (Daehan Jeguk; 대한 제국; 大韓帝國), or literally "Great Han Empire," modifying the country's old official name by replacing "Joseon" with "Han" and chaning Guk ("nation") to Jeguk ("empire").
When Korea came under Japanese control in 1910, the country reverted to the name Joseon (the official name being the Japanese Chosen (朝鮮)). During this period, many different groups outside of Korea worked or fought for independence. One group was the Shanghai-based Provisional Government of the Republic of Korea (Daehan Minguk Imshi Jeongbu; 대한 민국 임시 정부; 大韓民國臨時政府), adopting the name Daehan Minguk ("Republic of Korea"), a modified form of Daehan Jeguk ("Korean Empire").
Korea became independent with Japan's defeat in 1945. The country was then jointly divided into a Soviet occupation zone in the north and an American occupation zone in the south. The non-Communist Shanghai group had more influence in the south, which in 1948 became the "Republic of Korea," adopting the former provisional government's name of Daehan Minguk. Meanwhile, ex-Soviet Red Army major Kim Il-sung's Korean Workers' Party had more influence in the north, which in 1948 became the "Democratic People's Republic of Korea" (Chosŏn Inmin Minjujuŭi Konghwaguk; 조선 인민 민주주의 공화국; 朝鮮人民民主主義共和國), adopting "Joseon" (Chosŏn), a name with ancient and northern connotations.
Today, North Koreans use Chosŏn refer to Korea as a whole, and refer to the two countries specifically as Bukchosŏn (북조선; 北朝鮮; "North Chosŏn") and Namjosŏn (남조선; 南朝鮮; "South Chosŏn"). In contrast, South Koreans call Korea Hanguk and refer to North Korea as Bukhan (북한; 北韓; "North Han") and South Korea as Namhan (남한; 南韓; "South Han").
North Koreans never use Hanguk and South Koreans do not use Chosŏn (with a few exceptions, such as Chosun Ilbo, a South Korean newspaper). The Korean language is called Chosŏnŏ or Chosŏnmal in the North and Hangugeo or Hangungmal in the South. Chosŏngŭl is the North Korean name for what the South Koreans call Hangeul. The Korean Peninsula is called Chosŏn Pando in the North and Hanbando in the South.
When writing in English, a few authors write "north" and "south" in lowercase because they are not part of the countries' official names, and because of the belief that Korea should be considered as one connected socio-cultural nation. (In the same vein, official maps in both countries usually do not show the Military Demarcation Line that divides the two countries, giving the illusion that it is possible to travel freely back and forth between North and South.)
Newspapers in the People's Republic of China tend to refer to North Korea as Chaoxian (朝鮮) and to South Korea as Han'guo (韓國), similar to the situation in Japan, where North Korea is called Kita-Chosen (北朝鮮; "North Chosŏn") and South Korea Kankoku (韓國). The Republic of China, on the other hand, refers to North Korean as Beihan (北韓 "North Han") and South Korean as Nanhan (南韓 "South Han").
Both North and South Korea use the name "Korea" (or its equivalent in other western languages) when referring to their countries in English or other western languages. The name "Goryeo" (the source of "Korea") has therefore come back into fashion in Korean as an alternative, more or less neutral name for Korea. Thus, Russian and Central Asian citizens of Korean descent call themselves "Goryeo people" to avoid the North-South conflict. More recently, Koria (코리아; a back-translation from English) has also been used.
In English, until the end of the 19th century, the name "Corea" was used almost exclusively, with "Korea" only coming into common use at the turn of the 20th century. This has given rise to a widespread legend that says that the name "Korea" was created by the Japanese around the turn of the century. Since Japan was after Corea in alphabetical order, Japanese nationalists would have decided to change the upper-case "C" into a "K", thus changing "Corea" into "Korea." It is also said that this change occurred because the syllable ko (rather than co) is found in Japanese. However, "Korea" was also used along with "Corea" in English-language documents very early. The awareness of the alphabet and romanization in Japan (and Korea) is also questionable. The Japanese-modification theory, while widly in favour among nationalists, is dismissed as urban legend by most Koreanists.Ancient History
The Three Kingdoms
Unified Silla
Goryeo
Joseon
Japanese Colonial Period
After World War II
The Situation Today
Chinese and Japanese names
Western names