Ariell Zimran
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Like an Ink Blot on Paper: Testing the Diffusion Hypothesis of Mass Migration, Italy 1876-1920
with Yannay Spitzer
NBER Working Paper 30847 and CEPR Discussion Paper 17837
Rejected and resubmitted to the Review of Economic Studies

To explain the evolution of mass migration from Italy (1876-1920), we introduce the diffusion hypothesis, which augments traditional models of migration by allowing the spatial diffusion of migration over social networks in the country of origin. We test and validate the predictions of this theory using a new and comprehensive municipality- and district-level panel of emigration data over four decades. Italian migration began in a few separate epicenters from which it expanded gradually over time in an orderly spatial movement that dominated local push factors. While the main patterns that we document are parsimoniously explained by the diffusion hypothesis, they are difficult to rationalize by alternative theories. Confirming the diffusion hypothesis in the Italian case suggests that networks may be far more important than is commonly understood in shaping other movements of mass migration and may shape them in ways that have not previously been understood.