"Given the greater substitutability between immigrants and natives in the past, we would expect to find larger effects of immigrant arrivals on native wages during the Age of Mass Migration. Indeed, historical immigration flows appear to have a larger effect on the wages and employment opportunities of native workers than those found in contemporary geographic studies (subject to the caveat of differences in outcome variables and research design). Using cross-city variation in migrant flows in the 1910s, Goldin (1994) estimates that a one percentage point increase in the foreign-born share of the population reduced the wages of unskilled laborers and artisans by around 1.5 percent, with larger effects in the tradeable sector (clothing manufacturing and foundries). Boustan, Fishback, and Kantor (2010) find that internal in-migration in the 1930s had no effect on the wages of local workers, but did reduce work opportunities and access to relief jobs, a pattern that is consistent with the presence of sticky wages during the Great Depression. They create an instrument for migrant arrivals that relies on “push factors” from sending labor markets, including New Deal generosity and extreme weather events."