On April 20, 1980, Fidel Castro made an important contribution to the social sciences. His unexpected declaration that the port of Mariel would be temporarily open to any Cubans seeking to flee the island served as a natural experiment that has helped labor economists understand the impact of immigration. In his now classic paper, economist David Card convincingly showed that the massive influx of 120,000 Cubans increased the labor force of Miami by 7% yet had almost no impact on the employment or wages of natives.
This result is probably shocking to many, and certainly runs contrary to the popular but unfortunate myth that immigrants "steal our jobs". But while this study is an important result in the literature, it is not an isolated one. Most research on immigration shows small or zero impacts on unemployment and wages. This, however, does present something of a puzzle: if immigration increases labor supply, then why didn't wages fall and unemployment rise? How was it that the labor market in Miami was able to absord so many new workers?
One important reason is that immigrants aren't just workers, but also consumers. Economists Bodvarsson, Lewer, and Van den Berg studied the Mariel boatlift and found that migrants increased labor demand enough to offset the increase in labor supply so that there was no negative impact on natives that one might otherwise expect when labor supply increases drastically. This result shouldn't be surprising. Immigrants buy stuff, that means businesses sell more, and they need to expand and hire new workers.