According to Infoplease the Koreans, descended from Tungusic tribal peoples, are a distinct racial and cultural group. According to Korean legend, Tangun established Old Choson (朝鮮) in NW Korea in 2333 B.C., and the Korean calendar enumerates the years from this date.
There were traces of Chinese rule and the Koreans have resisted, from time to time, Chinese invasions. From 7th - 10th centuries, Korea was unified by the Silla Kingdom and flourished.
In 935 the Silla(新羅) dynasty was overthrown by Wang Kon who had established (918) the Koryo(高麗) dynasty (the name was selected as an abbreviated form of Koguryo and is the source of the name Korea).
Confucianism(孔子學說)—introduced from China during the Silla years and adapted to Korean customs—controlled the pattern of government. A coup in 1170 led to a period of military rule. In 1231, Mongol forces invaded from China, initiating a war that was waged intermittently for some 30 years. Peace came when Koryo accepted Mongol suzerainty, and a long period of Koryo-Mongol alliance followed. In 1392, Yi Songgye, a general who favored the Ming dynasty (which had replaced the Mongols in China), seized the throne and established the Choson dynasty.
There is also an interesting theory by Leon at his website that Koreans are a combination of Tungusic and Austronesian ethnicities.
The 1592 invasion by the Japanese shogun Toyotomi Hideyoshi(豊臣秀吉) was driven back by Choson and Ming forces, but only after six years of great devastation and suffering. Manchu invasions in the first half of the 17th cent. resulted in Korea being made (1637) a tributary state of the Manchu (滿洲) dynasty. Subsequent factional strife gave way, in the 18th century, to economic prosperity and a cultural and intellectual renaissance. Korea limited its foreign contacts during this period and later resisted, longer than China or Japan, trade with the West, which led to its being called the Hermit Kingdom.
In 1876, Japan forced a commerical treaty with Korea, and to offset the Japanese influence, trade agreements were also concluded (1880s) with the United States and European nations. Japan's control was tightened after the First Sino-Japanese War (1894–95) and the Russo-Japanese War (1904–5), when Japanese troops moved through Korea to attack Manchuria. These troops were never withdrawn, and in 1905 Japan declared a virtual protectorate over Korea and in 1910 formally annexed the country. The Japanese instituted vast social and economic changes, building modern industries and railroads, but their rule (1910–45) was harsh and exploitative. Sporadic Korean attempts to overthrow the Japanese were unsuccessful, and after 1919 a provisional Korean government, under Syngman Rhee (李承晚 1875～1965), was established at Shanghai, China.
A brief history in Chinese can be found HERE.