Abstract
The article traces recent political polarization to earlier institutional reforms opening up the political system to increased electoral competition. The increased influence of the rural majority led new political entrepreneurs to introduce welfare policies. The new polices were opposed by urban tax payers, setting off a process of policy driven polarization that drew on underlying cleavages in Thai society. Empirical tests based on voting patterns in the most recent general election using a seemingly unrelated regression model provide support for the hypothesis of policy driven political polarization. The analysis highlights the vulnerability to increased polarization after introduction of institutional reforms that alter the balance of power between dfferent parts of the electorate. It is noted that neither reversals of institutional changes nor policy reversals are effective for stopping negative cycles of increased polarization, whereas inclusive and policy based public debate can lower polarization.