Why did the United States move from having nearly open borders from the 1840s to the 1870s to passing the Chinese Exclusion Act in 1882, the first law in American history to ban people from entering the United States solely based on race? We argue that the standard story of nativist backlash based on wage pressure explains the demand for immigration restrictions, but not their timing or their racial focus. The demand for immigration restrictions was largely inchoate until the political restructuring that followed the Civil War. Finding themselves uncompetitive in much of the country, the Democrats seized on immigration restrictions, most notably in growing California, as a wedge issue. Chinese residents were unable to vote, thus making restrictions on Chinese entry an especially effective strategy in political economy.