Realism, institutional-liberalism and constructivism are state-centric. State formation and consolidation as a unitary actor that concentrates sovereignty, population, territory, autonomy, and authority is a product of modernity. This essay first address how state centrism evolved in the principal theories in IR, then present the strengths and limitations of the state centric approach as a unit of analysis, followed by an analysis of the incorporation of new units of analysis such as transnational networks or subnational actors. Recently, there is a development of new unit of analysis, which shows a flow back where the subnational level and individual levels of analysis influencing international relations.