How has European integration developed in reaction to the Russo-Ukrainian war? This chapter presents a “bordering” analysis of “integration through war”. In this perspective, integration has two dimensions. First, and corresponding to the community-building dimension of polity formation, integration consists in the opening of boundaries for subjects and objects. Second, and corresponding to capacity building, it consists in the centralisation of control over the EU’s external boundaries. We examine the level and change of boundary closure and control in response to the war both within the EU and between the EU and Ukraine across four functional domains and for more than thirty categories of subjects and objects from 2013 to the first half of 2023. EU-Ukrainian boundaries, we find, have gradually opened after the 2014 Russian attack, and we observe a sharp decline in boundary closure in response to the 2022 invasion. We also show that this opening in 2022 has been particularly remarkable for the entry of persons in the economic and political domains. By contrast, boundary control has changed only slightly. We conclude that, at least in the initial period, “integration through war” has occurred primarily in the community building and less so in the capacity-building dimension of integration.