UC San Diego

Why do capable states sometimes possess seemingly inefficient militaries that leave them vulnerable to security threats? Practitioners have long maintained that a full spectrum combined-arms military is the best defense in an unpredictable and anarchic international environment. Yet capable states often either forgo some vital defense capabilities, like the US omitting minesweepers from its planned 600 ship navy in the 1980s, or overproduce some defense capabilities, like Albania developing coastal patrol vessels with a range of 1,750 miles despite having a coastline that is roughly one tenth that size. Are states with seemingly inefficient militaries simply making mistakes? I argue that vulnerable force structures are not just the result of poor planning or resource constraints; rather, these observed “inefficiencies” are often a strategically motivated decision to specialize one’s force structure. While there are certainly advantages to a diversified military portfolio, states can engage in strategically motivated functional differentiation by specializing their militaries when they engage in cooperative security alignments. When a collection of states facing a similar threat environment are able to minimize the risk of defection and ensure effective coordination, they can engage in a division of labor where each state individually specializes in different military capabilities that, when brought together, still comprise a full spectrum military force. I substantiate these arguments with evidence from a new dataset on the distribution of military capabilities from 1970-2020 and find that 1) states in cooperative security alignments have more specialized militaries, and 2) cooperative security alignments with more closely aligned interests and higher vertical integration have a higher division of labor.