South Koreans voted for a Constituent National Assembly under United Nations supervision while the peninsula was still divided after Japanese colonial rule. The new assembly’s central job was to write a constitution and design a national government for the South. This election set the political stage for Syngman Rhee’s rise to the presidency.
The Constituent National Assembly adopted and proclaimed South Korea’s first constitution, establishing a presidential system with a National Assembly. This document provided the legal foundation for the new state and its elections. It is commemorated as Constitution Day in South Korea.
Using the new constitution’s rules, the National Assembly held an indirect election for president and vice president. Syngman Rhee won decisively, making him the leading figure of the emerging First Republic. This election helped formalize executive power at a moment of intense political instability.
The Republic of Korea (South Korea) was formally proclaimed, marking the start of the First Republic period. The new government claimed legitimacy for the southern part of the peninsula as Cold War tensions hardened division with the North. State-building now moved from military occupation toward independent governance.
South Korea enacted the National Security Law, intended to counter North Korean influence and internal communist activity. In practice, the law also became a tool used by the Rhee government to suppress political opponents and restrict speech and organization. The law’s early use shaped the First Republic’s authoritarian direction.
Kim Gu, a prominent independence activist and political leader, was assassinated in Seoul. His death removed a major nationalist figure who had opposed creating a separate government in the South. The assassination deepened political polarization during the early years of the First Republic.
North Korean forces crossed the 38th parallel and invaded South Korea, starting the Korean War. The invasion threatened the survival of the new South Korean state and brought in a United Nations Command to defend it. The war transformed the First Republic into a wartime government and intensified internal security crackdowns.
As North Korean advances pushed South Korean forces south, the national government relocated and Busan became the wartime seat of government. This move reflected the emergency conditions of the conflict and the struggle to keep state institutions functioning. Busan’s role as wartime capital became a major symbol of South Korea’s survival during the war.
Facing a legislature that could block his reelection, Rhee pushed through a constitutional change to elect the president by popular vote. South Korea then held its first direct presidential election during the war, and Rhee won a large majority. The episode showed how constitutional rules were increasingly reshaped to secure executive power.
After two years of negotiations, an armistice halted major fighting and established the Korean Demilitarized Zone (DMZ). The agreement ended open warfare but did not create a peace treaty, leaving the conflict unresolved. Rhee opposed a ceasefire that left Korea divided, a stance that affected South Korea’s politics and diplomacy afterward.
South Korea and the United States signed a mutual defense treaty soon after the armistice. The pact committed both countries to respond to external attack and allowed for continued U.S. troop presence in South Korea. This alliance became a cornerstone of South Korea’s security policy during and after the First Republic.
A constitutional amendment—often called the “Rounding-off” amendment—was passed, allowing the first president to run for another term. This change weakened term-limit protections and reinforced the concentration of power around Rhee and his supporters. It set up the political conditions for high-stakes elections in the mid-to-late 1950s.
South Korea held another direct presidential election, and Rhee won again. In the same election, opposition candidate Chang Myon won the vice presidency, showing real public dissatisfaction with the ruling party. The split result increased tension between the government and a growing democratic opposition.
The Progressive Party, led by Cho Bong-am, was dissolved after being accused of illegal activities under the National Security Law framework. The case signaled that organized political alternatives—especially those advocating peaceful approaches to reunification—could be treated as security threats. This further narrowed space for lawful opposition during the First Republic.
Presidential and vice-presidential elections were held, but widespread allegations of fraud—especially in the vice-presidential race—sparked public outrage. With Rhee effectively unopposed for president, the credibility of the vote became the core issue. The crisis quickly expanded beyond election complaints into a broader movement against authoritarian rule.
Student-led protests grew into mass demonstrations after police violence, including unrest centered in Masan and Seoul. The National Assembly moved to demand Rhee’s resignation, and Rhee submitted his resignation shortly afterward. This ended the First Republic and opened the way for a new constitutional order under the Second Republic.
First Republic under Syngman Rhee (1948–1960)