The right answer is limit the number of immigrants who could enter the US from each country.
During the 1920s the concerns about foreign radicals invading the US created new efforts to restrict immigration. The first result was the Immigration Act of 1921 which restricted European arrivals each year to 3 percent of the total number of each nationality represented in the 1910 census. Still, with the need of strengthening the law, The Immigration Act of 1924 reduced the number to 2 percent based on the 1890 census, which included fewer of the “new” immigrants from southern and eastern Europe. This law set a permanent limitation, which became effective in 1929, of slightly over 150,000 new arrivals per year based on the “national origins” of the U.S. population as of 1920. The intention was clear to tilt the balance in favor of immigrants from northern and western Europe, who were assigned about 85 percent of the total. The law completely excluded people from East Asia.