Clustering analysis of European countries' defense policies before and after the Russia-Ukraine war: Identifying strategic trends

The Russia-Ukraine War transformed Europe not only by increasing defense budgets, but by pushing countries toward different defense profiles. This study examines the structural change in European defense policies between 2000 and 2025 through multidimensional indicators and a data-driven clustering approach. Using data from 28 European countries, including Türkiye, the analysis considers defense burden, equipment spending, total defense expenditure, military personnel, energy import dependency, real expenditure change, public debt, infrastructure investment, per capita defense spending, and domestic procurement. The data were divided into three periods—2000–2013, 2014–2021, and 2022–2025—reflecting major geopolitical ruptures in European security architecture. Country averages were calculated for each period, standardized with Z-scores, and classified using K-Means clustering. The elbow method and silhouette coefficient were used to determine the number of clusters, while PCA-based visualizations supported interpretation. The findings show that European defense architecture displayed a dual structure in the first two periods, consisting of a narrow high-capacity core and a broader peripheral group. After 2022, however, this structure fragmented into five distinct strategic clusters. Rapidly rearming frontline countries, major defense economies, fragile peripheral countries, and selectively modernizing countries became more clearly differentiated, while Türkiye occupied a distinctive position due to its high personnel capacity and domestic procurement structure. Overall, the study shows that geopolitical shocks did not produce homogeneous militarization across Europe. Instead, they generated a fragmented and multilayered defense order shaped by threat perceptions, economic capacity, and structural vulnerabilities. The thesis therefore offers a data-driven framework for evaluating European defense policies through multidimensional defense profiles rather than isolated indicators.