Complex sentence: Jin-Heon Jung argues that there has been a polarization in the South Korean society since start of the Sunshine Policy as polarization between states decreased, the ideological and political polarization inside South Korea increased.
Split into simpler sentences: Jin-Heon Jung argues that there has been a polarization in the South Korean society since start of the Sunshine Policy. As polarization between states decreased, the ideological and political polarization inside South Korea increased.