Economic considerations typically dominate discussions surrounding the EU and Southeast Asia Free Trade Agreements. Yet, this chapter argues that national identity plays a more fundamental role in shaping these relations, though underexplored. Most existing analyses focus on economic metrics, such as trade balances and market access. However, to fully grasp the dynamics of these agreements, it is crucial to consider the role of nationalism. This chapter introduces nationalism as a critical perspective, offering a distinct lens through which to view the world. While much political science research traditionally frames nationalism as an ideology of the extreme right, this work contends that nationalism is, in fact, a form of national consciousness—a primary framework through which citizens interpret their place in the global order. In this chapter, nationalism is defined, and central research debates are explored. It discusses how nation-states, as imagined communities, evolved into powerful realities underpinned by institutionalised histories, norms, and values that become their raison d’être shaping the lived experiences of citizens. Political elites actively maintain these elements, with the defence of national interests becoming a key source of their legitimacy. The chapter then delves into national identity formation in post-colonial states, highlighting nationalism’s central role as an organising force in international relations.