Democracy and polarization in the National Assembly of the Republic of Korea

TL;DR

This study examines the evolution of political polarization in South Korea's National Assembly over 70 years, revealing shifts from high polarization to multi-dimensionality, and compares it with US Congress patterns to assess the median-voter hypothesis.

Contribution

It provides a long-term empirical analysis of legislative polarization dynamics in Korea and contrasts it with US data to evaluate the median-voter hypothesis's applicability.

Findings

High polarization in Korea before democratization

Sharp decrease in polarization after 1987

Increasing multi-dimensionality in Korean politics over time

Abstract

The median-voter hypothesis predicts convergence of party platforms across a one-dimensional political spectrum during majoritarian elections. Assuming that the convergence is reflected in legislative activity, we study the time evolution of political polarization in the National Assembly of the Republic of Korea for the past 70 years. By projecting the correlation of lawmakers onto the first principal axis, we observe a high degree of polarization from the early 1960's to the late 1980's before democratization. As predicted by the hypothesis, it showed a sharp decrease when party politics were revived in 1987. Since then, the political landscape has become more and more multi-dimensional under the action of party politics, which invalidates the assumption behind the hypothesis. For comparison, we also analyze co-sponsorship in the United States House of Representatives from 1979 to 2020, whose correlation matrix has been constantly high-dimensional throughout the observation period. Our analysis suggests a pattern of polarization evolving with democratic development, from which we can argue the power and the limitation of the median-voter hypothesis as an explanation of real politics.