Between 1890 and 1924, about 23 million people migrated from Eastern and Southern Europe. In 1900, 14 percent of the American population was foreign born, compared to 8 percent a century later. Passports were unnecessary and the cost of crossing the Atlantic was just $10 in steerage.

European immigration to the United States greatly increased after the Civil War, reaching 5.2 million in the 1880s then surging to 8.2 million in the first decade of the twentieth century. In 1907 alone, 1.285 million arrived. By 1900, New York City had as many Irish residents as Dublin. It had more Italians than any city outside Rome and more Poles than any city except Warsaw. It had more Jews than any other city in the world, as well as sizeable numbers of Slavs, Lithuanians, Chinese, and Scandinavians.

Unlike earlier immigrants, who mainly came from northern and western Europe, the "new immigrants" came largely from southern and eastern Europe. Largely Catholic and Jewish in religion, the new immigrants came from the Balkans, Italy, Poland, and Russia.