Over the last thirty years, three critical events caused significant changes in the strategic environment of European states, resulting in significant adjustments of their defence policies. After the fall of the Berlin Wall, out-of-area crisis management operations became an important objective of European militaries, while territorial defence faded into the background. However, after Russia’s 2014 annexation of Crimea and war in Eastern Ukraine, and especially after its 2022 invasion of Ukraine, territorial defence again became the most important objective for European armies. The project aims to map and explain the different ways in which European states have adapted their defence policies to these changes in their strategic environment.