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Leaning on Legionnaires:
Why Modern States Recruit Foreign Soldiers

International Security (July 2021), Vol. 46, No. 1, pp. 147-195.

Why do modern states recruit legionnaires—foreigners who are neither citizens nor subjects of the country whose military they serve? Rather than exclusively enlist citizens for soldiers, for the past two centuries, states have mobilized legionnaires to help wage offensives, project power abroad, and suppress dissent. A supply-and-demand argument explains why states recruit these troops, framing the choice to mobilize legionnaires as a function of political factors that constrain the government’s leeway to recruit domestically and its perceptions about the territorial threats it faces externally. A multimethod approach evaluates these claims, first by examining an original dataset of legionnaire recruitment from 1815 to 2020, then by employing congruence tests across World War II participants, and finally by conducting a detailed review of a hard test case for the argument—Nazi Germany. The prevalence of states’ recruitment of legionnaires calls for a reevaluation of existing narratives about the development of modern militaries and provides new insights into how states balance among the competing imperatives of identity, norms, and security. Legionnaire recruitment also underscores the need to recalibrate existing methods of calculating net assessments and preparing for strategic surprise. Far from bound to a state’s citizenry or borders, the theory and evidence show how governments use legionnaires to buttress their military power and to engineer rapid changes in the quality and quantity of the soldiers that they field.


Introducing the Foreign Recruitment Dataset:
Legionnaires and the Spectrum of Military Manpower

This article introduces the foreign recruitment dataset, documenting how governments have supplemented their citizen-based armies with legionnaires—individuals who are neither citizens, colonial subjects, or co-ethnics of the government that they serve. Contrary to the expectations of existing political science research, the recruitment of legionnaires has been both an enduring and an expanding feature of how governments build their military power. 

This project details historical trends in how governments have enlisted foreigners in the modern age (1815 - 2020), including the growth of these policies over time, the methods states have adopted in fielding these troops, the types of regimes that have enlisted legionnaires, and patterns of naturalization. The article closes by outlining research questions where the addition of this data can add unique insight, and identifies the implications for ongoing scholarly debates.