Abstract The overriding research questions addressed here involve to what extent alternative samples of North Atlantic Treaty Organization (NATO) and European allies free ride on other allies' military expenditure (ME) during the post–Cold War era. In so doing, we indicate how spatial and spatiotemporal considerations affect this free riding. For 1992–2023, the article estimates NATO defense demands under four spatial-weighting ME spillin schemes and finds that free riding was prevalent. Those findings are then contrasted with the case in which both spatial and temporal lags on ME are allowed, leading to much reduced short-run, spatial-based free riding, followed by increasing free riding over time as defense-spending bureaucratic inertia dissipated. With spatial and spatiotemporal spillins, the first Trump administration's term was associated with reduced NATO free riding. We then focus on two alternative European samples to address the counterfactual of how greater European defense self-reliance is apt to impact European free riding in the absence of a US and Canadian defense commitment. When the NATO sample excludes the United States and Canada, NATO European allies' free riding was much reduced, disappearing for three spatial-weighting schemes. Notably, free riding disappeared altogether for a pan-European sample of NATO and non-NATO countries. Those results suggest that, if the European countries succeed in raising their defense spending during Trump's second term, free riding within Europe will not likely undo their efforts. Finally, for the post-Crimean period (2014–2023), we find that NATO defense spending did not display short- or long-run free riding.
George et al. (Tue,) studied this question.