Widely remembered as a time of heated debate over the westward expansion of slavery, the 1850s in the United States was also a period of mass immigration. As the sectional conflict escalated, discontented Europeans came in record numbers, further dividing the young republic over issues of race, nationality, and citizenship. The arrival of German-speaking "Forty-Eighters," refugees of the failed European revolutions of 1848-49, fueled apprehensions...