We investigate external and domestic political influences on defence burden of the 28 EU member states, based on time-series cross-section data from 1993 to 2017. Our research is one of the most comprehensive studies on EU members' defence, as it includes many potential explanations. Our findings do not support freeriding by EU members, both NATO allies and non-NATO members, on US commitment in the defence and security field. Relatedly, NATO membership does not come up in the analysis as an instantaneous guarantee for an effective special relationship with the US. However, there is evidence of freeriding by EU members not belonging to the Alliance on EU-NATO member states. Domestic political factors are also important: right-wing parties in government are associated with heavier defence burden, while upcoming elections tend to reduce it. In general, we find that to provide an accurate explanation of military spending, one needs to take into account a multitude of different factors and, moreover, pay attention to conditional effects.