Noah Smith discusses:
… the impact of immigration on the native-born. Economist David Card famously researched this in the 1990s, when he looked at what happened to Miami’s economy after the Mariel boatlift in which about 125,000 Cubans came to the U.S. He found that the flood of refugees — which increased Miami’s labor force by about 7 percent — had no adverse impacts on the local labor market.
It’s possible that the long-term effect of admitting refugees might be even more positive than the short-term boost. According to the theory of economic agglomeration, population density encourages companies to relocate to a region in order to gain access to customers. Just look at the eagerness of U.S. companies to invest in China.