From 1915 to 1930, 1.5 million African Americans moved from the southern US to northern urban centres. This column uses that shift as a historical case study, investigating how the appearance of a new migrant group affects the integration of previous generations of immigrants. It finds that the arrival of African Americans increased the effort exerted by Southern and Eastern Europeans to assimilate, but that Western and Northern Europeans, who were regarded as culturally closer to the native-born white population, had an easier time integrating.