With declining Chinese power and a weakened domestic posture at the end of the 19th century, Korea was open to Western and Japanese encroachment. In 1910, Japan began a 35-year period of colonial rule over Korea. As a result of Japanís efforts to supplant the Korean language and culture, memories of Japanese annexation still recall fierce animosity and resentment, especially among older Koreans. Nevertheless, import restrictions on Japanese movies, popular music, fashion, and the like have been lifted, and many Koreans, especially the younger generations, eagerly follow Japanese pop culture.

Japanís surrender to the Allied Powers in 1945, signaling the end of World War II, only further embroiled Korea in foreign rivalries. Division at the 38th Parallel marked the beginning of Soviet and U.S. trusteeship over the North and South, respectively. On August 15, 1948 the Republic of Korea (R.O.K.) was established, with Syngman Rhee as the first President; on September 9, 1948, the Democratic Peopleís Republic of Korea (D.P.R.K.) was established under Kim Il Sung.

On June 25, 1950, North Korean forces invaded South Korea. Led by the U.S., a 16-member coalition undertook the first collective action under United Nations Command (UNC). Following Chinaís entry on behalf of North Korea later that year, a stalemate ensued for the final two years of the conflict. Armistice negotiations, initiated in July 1951, were ultimately concluded on July 27, 1953 at Panmunjom, in the now Demilitarized Zone (DMZ). The Armistice Agreement was signed by representatives of the Korean Peopleís Army, the Chinese Peopleís Volunteers, and the U.S.-led United Nations Command (UNC). Though the R.O.K. supported the UNC, it refused to sign the Armistice Agreement. A peace treaty has never been signed. The war left almost three million Koreans dead or wounded and millions of others homeless and separated from their families.

In the following decades, South Korea experienced political turmoil under autocratic leadership. President Syngman Rhee was forced to resign in April 1960 following a student-led uprising. The Second Republic under the leadership of Chang Myon ended after only one year, when Major General Park Chung-hee led a military coup. Parkís rule, which resulted in tremendous economic growth and development but increasingly restricted political freedoms, ended with his assassination in 1979. Subsequently, a powerful group of military officers, led by Lieutenant General Chun Doo Hwan, declared martial law and took power.

Throughout the Park and Chun eras, South Korea developed a vocal civil society that led to strong protests against authoritarian rule. Composed primarily of students and labor union activists, protests movements reached a climax after Chunís 1979 coup and declaration of martial law. A confrontation in Gwangju in 1980 left at least 200 civilians dead. Thereafter, pro-democracy activities intensified even more, ultimately forcing political concessions by the government in 1987, including the restoration of direct presidential elections.

In 1987, Roh Tae-woo, a former general, was elected president, but additional democratic advances during his tenure resulted in the 1992 election of a long-time pro-democracy activist, Kim Young-sam. Kim became Koreaís first civilian elected president in 32 years. The 1997 presidential election and peaceful transition of power marked another step forward in Koreaís democratization when Kim Dae-jung, a life-long democracy and human rights activist, was elected from a major opposition party. The transition to an open, democratic system was further consolidated in 2002, when self-educated human rights lawyer, Roh Moo-hyun won the presidential election on a "participatory government" platform.