This article employs a postcolonial historical sociological approach to studying state formation in Iraq between 1914–24. In doing so, it synthesises insights from the ‘historical’ and ‘imperial’ turns in International Relations (IR), to understand the state as a processual and relational entity shaped by the imperial relations through which it emerged. Drawing on the case of Iraq, this article demonstrates how British imperial relations (‘international’) interlaced with anti-colonial struggles (‘domestic’) to foster a historically specific pattern of Iraqi state formation. In making these claims, this article contributes to bridging IR's analytical divide between ‘international’ and ‘domestic’ spaces, while undermining IR's universalist assumptions about the ‘spread’ of the state from Europe to the Arab world. Rather, this article demonstrates that the imperial encounter was constitutive of the type of state that emerged, thereby highlighting the agency of anti-colonial struggles in producing historically specific patterns of state domination.