Modern states occupy a critical position at the intersection of international systems and domestic societies. National autonomy enables countries to independently navigate inter-state relations within the global system and make autonomous decisions in response to the needs of diverse social groups at the domestic level. The construction of a modern state involves the integration of both nation-state and democratic-state models. National autonomy plays a pivotal role in securing this construction. This paper highlights the relationship between national autonomy and modern state-building in Southeast Asia through a comparative analysis of Singapore and the Philippines. Singapore, characterized by strong autonomy, has effectively advanced both nation-state and democratic-state development. In contrast, the Philippines, marked by weak or absent autonomy, faces significant challenges in constructing a cohesive nation-state and functioning democracy. The degree of national autonomy in developing countries directly influences the success or failure of their state-building efforts and governance.