If you look at even Wikipedia they show that South Korea has spent its time as a dictatorship

Korea Kingdom (Until 1910)

Korea under Japanese rule (1910 to 1945)

United States Army Military Government in Korea (1945–1948)

First Republic of Korea (1948–1960): Unitary presidential republic under an authoritarian dictatorship

Second Republic of Korea (1960–1961) Unitary parliamentary republic

Third Republic of Korea (1963–1972) Unitary presidential republic under an authoritarian military dictatorship

Fourth Republic of Korea (1972–1981) Unitary semi-presidential republic under an authoritarian military dictatorship

Fifth Republic of Korea (1981–1988) Unitary semi-presidential republic under an authoritarian military dictatorship

They are currently on the Sixth Republic of Korea listed as a Unitary presidential republic