The impact of violence during the Mexican Revolution on Migration to the United States

with Ed Kosack and Zach Ward

 

Project funded by the 2020 Carnevali Research Grant, Economic History Society.

Media coverage: The Long Run, Yale Economic Growth Center

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The number of individuals forcibly displaced, for reasons such as conflict and violence, has more than doubled from around forty million in 2011 to nearly ninety million in 2021, and the trend is expected to continue to increase in the coming year. Temporary conflicts might fundamentally shape migration flows depending on the magnitude and persistence of the migration response.

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In this paper, we examine the migration response to violence during The Mexican Revolution (1910-1920), one the deadliest conflicts in world history: it is estimated that 1.4 million died—about 10% of the population—and another 350,000 fled north across the border. To do so, we collect two novel data sources that are unique in terms of frequency and completeness. First, we collect monthly data on migration flows between 1910 and 1920 from individual border crossings registered at 24 entry points along the US-Mexico border. Second, we digitize daily data on insurgency events from military reports compiled in the "Military History of the Mexican Revolution." We link these two sources together at the municipa lity level (roughly equivalent to a county in the United States) and construct a month-by-municipality panel spanning from November 1910 to December 1915. 

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To examine the impact of violence on migration, we use a fully flexible event-study design that estimates differences in monthly migration rates between units (municipalities) that experienced a violent event and those that had not yet experienced or never experienced violence. We find that violence led to a significant, but temporary, increase in migration: in the first and second month after the event, migration increased by 60% relative to pre-event levels. The rate of migration fell to a 30% increase over baseline in the third and the fourth months, and after five months, the rate of migration had reverted back to pre-event levels. This finding, however, masks heterogeneity in treatment effects across population groups in terms of timing, magnitude, and persistence. The results show that male migration rates returned to pre-event levels after the second month, while migration rates among children and women increased permanently. We provide evidence that these effects changed the sex composition of the migration flow during the period of analysis. Among the elderly population, we observe a one-month delayed, relatively weak migration response.

 

In addition, we examine specific mechanisms for the magnitude, persistence, and timing of the migration response. We find that the increase in migration rates was significantly larger in municipalities where historical and recent migrant networks were present, and that there were permanent migration increases in response to events where the victor remained in the conflict location. Our analysis also shows that differences in local communication and transportation infrastructure played an important role in shaping the timing of migration.   

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Our main contribution is to use high-frequency data to more precisely identify the dynamics and timing of migration caused by generalized violence. Most studies on forced migration or displaced people examine conflicts characterized by persecution, where the group that is displaced is also persecuted. We also improve our historical understanding of the Mexican Revolution and the Mexico-US migration history. We know from anecdotal and indirect evidence that migration flows from Mexico to the United States increased during the Mexican Revolution. However, we are the first to provide direct, quantitative evidence on the impact that this conflict had on the scale and composition of flow at the local level.