This dissertation project explores how institutions have shaped dimensional structure in East Asian legislatures, including Hong Kong, South Korea, and Taiwan in the past two decades. The major issues dividing the left and right in East Asia are not about economic in nature, but rather structured by legislators' preferences vis-`a-vis democratization and the relationship with Beijing in Hong Kong, the geo-security issue in South Korea, and the Taiwanese or Chinese identity issue in Taiwan. This dissertation provides either the first or some of the very first empirical evidence of the dimensional structure of the three East Asian politics. By drawing from the literature on political parties, electoral laws, and legislative agenda dynamics, my dissertation also explains how legislators facing different institutional incentives align differently either with or against the main political cleavage.