Behavioural and Political Factors Enabling Estonia to Commit to 5% Defence Expenditure: A Behavioural Science Case Study

Abstract

Chronic underinvestment into defence among most NATO allies has led to a security vacuum in Europe. Despite repeated declarations and commitments to increase defence investments, these intentions have often failed to translate into actual expenditure. A handful of NATO countries, however, have consistently exceeded agreed targets which warrants further analysis. Drawing on elite interviews with Estonian decision-makers, this thesis explains the behavioural and political factors that enabled Estonia to increase defence expenditure to over 5% of GDP al-ready before such a target was established among NATO members. Using the Theory of Planned Behaviour as an analytical framework, the findings suggest that elevated threat perceptions alone are insufficient to explain increased defence investments. Instead, the decision emerged from the interaction of multiple factors shaping behavioural intentions. Positive attitudes towards defence spending were driven by perceived military necessity, informed by threat perceptions and expert military advice. These were supported by favourable domestic and international norms, including strong alignment with NATO commitments. At the same time, perceived behavioural control was enhanced by increased fiscal flexibility, through anticipated changes to EU deficit rules, which enabled further deficit spending for defence. Crucially, the translation of behavioural intention into actual policy was enabled by prime-ministerial leadership, which acted as the key mechanism in advancing the decision despite constraints. This thesis contributes to broader international relations research by applying a behavioural sci-ence perspective to policymakers’ behaviour in the formulation of defence policy with geopolitical implications. It further outlines a set of policy recommendations for nations to increase defence spending and proposes a potential impact study to assess which factors are most influential in shaping decision-makers’ willingness to increase defence investments.