  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 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 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. Our finding thus suggests the power and limitation of the
median-voter hypothesis as an explanation of real politics.
