Territory and territoriality lie at the heart of both world politics and International Relations (IR) theory. In terms of IR theory’s geographical assumptions, one of the most influential studies to date has been political geographer John Agnew’s 1994 article on the ‘the territorial trap’ (TTT). While Agnew’s original insights and subsequent research has reached canonical status in political geography, mainstream IR scholarship has yet to fully engage TTT. Political geographers, in turn, have largely dealt with the consequences of TTT for our understanding of world politics. This study offers the first detailed account of the origins of TTT, which are hidden in broad daylight in IR’s own history. The origins of TTT and mainstream IR are intertwined in terms of two dynamics: the racist and colonial origins of IR, and the selective nationalistic ontology that dominated IR especially in the first half of the 20th century. The arguments offered in this study have a wide variety of implications for problematising the ways in which IR-as-epistemological-community approaches territory and territoriality as well as our understanding of the origins and evolution of the present-day global territorial order.