The UK faces the gravest security environment since the Second World War, and yet its institutions remain unable to fully adapt to the seriousness of the challenge. It is clear that we are no longer in a time of peace, but the political incentives to adequately project deterrence to our adversaries, and prepare the nation for the realities of what could come, are failing to drive transformative change.

Why have European leaders repeatedly advocated an EU defence capacity yet so often fallen short of their ambitions, and how does EU defence function alongside NATO? Focusing on three defining periods of EU defence integration (1999, 2004, and 2016), this paper draws on archival material and elite interviews to reassess when and why integration advances. Building on insights from psychological approaches in International Relations, it shows that major institutional steps tend to cluster around moments of acute political strain rather than clear shifts in the external threat environment.