Syngman Rhee in the context of "First Republic of Korea"

The Korean War (25 June 1950 – 27 July 1953) was an armed conflict on the Korean Peninsula fought between North Korea (Democratic People's Republic of Korea; DPRK) and South Korea (Republic of Korea; ROK) and their allies. North Korea was supported by China and the Soviet Union, while South Korea was supported by the United Nations Command (UNC) led by the United States. The conflict was one of the first major proxy wars of the Cold War.

After the end of World War II in 1945, Korea, which had been a Japanese colony for 35 years, was divided by the Soviet Union and the United States into two occupation zones at the 38th parallel, with plans for a future independent state. Due to political disagreements the zones formed their own governments in 1948. North Korea was led by Kim Il Sung in Pyongyang, and South Korea by Syngman Rhee in Seoul; both claimed to be the sole legitimate government of all of Korea. On 25 June 1950, the Korean People's Army (KPA), equipped and trained by the Soviets, launched an invasion of the south. In the absence of the Soviet Union's representative, the UN Security Council denounced the attack and recommended member states to repel the invasion. UN forces comprised 21 countries, with the United States providing around 90% of military personnel.

Korean reunification is the hypothetical unification of North Korea and South Korea into a singular Korean sovereign state. The process towards reunification of the peninsula while still maintaining two opposing regimes was started by the June 15th North–South Joint Declaration in June 2000, was reaffirmed by the October 4th Declaration in October 2007 and the Panmunjom Declaration in April 2018. In the Panmunjom Declaration, the two countries agreed to work to officially end the Korean conflict in the future.

Prior to the First World War and Korea under Japanese rule (1910–1945), all of Korea had been unified as a single state for over a millennium, notably under the Goryeo and Joseon dynasties (the latter of which was declared the Korean Empire in 1897). After the end of World War II in 1945 and during the beginning of the Cold War, Korea had a unified government, the People's Republic of Korea. However, this would be brief and serve as the last government, as Korea was divided into two countries along the 38th parallel (now the Korean Demilitarized Zone) in 1948. After World War II, North Korea was occupied by the Soviet Union, and later administered by the Workers' Party of Korea under Kim Il Sung. South Korea was occupied by the United States, later becoming independent under dictator Syngman Rhee. Both governments of the two new Korean states claimed to be the sole legitimate government of all of Korea. The Korean War, which began in June 1950, ended in a stalemate in July 1953.

The Second Republic of Korea (Korean: 제2공화국; RR: Je-i Gonghwaguk; lit. "Second Republic") was the government of South Korea from June 1960 to May 1961.

The Second Republic was founded months after the April Revolution mass protests against President Syngman Rhee, succeeding the First Republic and establishing a parliamentary government under President Yun Posun and Prime Minister Chang Myon. The Second Republic ended Rhee's authoritarianism and repression, formed a liberal democracy, and formulated the first Five-Year Plans to develop the formerly neglected economy. After thirteen months it was overthrown by the South Korean Army in the May 16 coup led by Park Chung Hee. The Second Republic was replaced by a provisional military government under the Supreme Council for National Reconstruction, leading to the Third Republic of Korea.

The April Revolution (Korean: 4.19 혁명), also called the April 19 Revolution or April 19 Movement, were mass protests in South Korea against President Syngman Rhee and the First Republic from April 11 to 26, 1960, which led to Rhee's resignation.

Protests opposing Rhee were started by student and labor groups in the southeastern port city of Masan on April 11. The protests were triggered by the discovery of the body of a local high school student killed by police during demonstrations against rigged elections in March. Popular discontent had arisen due to Rhee's autocratic rule, corruption, use of violence against political opposition, and uneven development of South Korea. The Masan discovery led to large student protests in Seoul, which were violently suppressed; a total of 186 people were killed during the two weeks of protest. Rhee resigned on April 26 before fleeing to exile in the United States, and was replaced by Yun Posun, beginning the transition to the Second Republic of South Korea.

Presidential and vice presidential elections were held in South Korea on 20 July 1948, following the Constitutional Assembly elections in May. The president was to be elected by the members of the National Assembly, as instructed by the 1948 Constitution. Of the 198 members of the National Assembly, 196 were present for the vote. A candidate required two-thirds of the votes cast to win. Syngman Rhee was elected with 180 votes, and took over the government to oversee the transfer of power from the United States Army Military Government in Korea.

An important role was played in the run-up to the election by the dispute between Rhee and Kim Ku over the issue of establishing a separate government in the southern part of Korea, instead of including the communist-controlled north. Kim rejected the idea of separate elections, and had boycotted the Constitutional Assembly elections in May, instead campaigning for a united Korea. He also split from the National Alliance for the Rapid Realization of Korean Independence to form the Korea Independence Party. Despite Kim's refusal to take any part in a South-only government and therefore in this election, 13 members cast their votes for Kim.

The Constituent National Assembly (Korean: 대한민국 제헌 국회) of South Korea was the constituent and first National Assembly of the Republic of Korea. Consisting of 200 members elected for the election on May 10, 1948, it was formed on May 31, 1948, and served for two years until May 30, 1950. Syngman Rhee was invited to be the first interim chairman and the National Assembly chairman, and Sin Ik-hui and Kim Dong-won [ko] were elected as vice chairmen.

Formed under the mandate of the United Nations General Assembly, the constituent assembly ratified the constitution of the Republic of Korea and voted Syngman Rhee as the first president of the Republic.