American wars have provided both opportunities and difficulties for immigrants. On the one hand, conflict has given immigrants a chance to demonstrate their loyalty to the United States. On the other hand, immigrants have faced problems when hostilities arise between the United States and their native country or when, for various reasons, American citizens suspect that their immigrant neighbors do not fully support the military effort.

In the nineteenth century America's first major immigrant groups, the Irish and the Germans, faced this dilemma. The Irish arrived in large numbers after the end of the War of 1812. The Great Potato Famine of 1845 to 1849 brought the number of Irish in the United States to 1.6 million by 1860. These Irish were overwhelmingly Catholic and often poor. They lived in the worst neighborhoods, did the least desirable work, and were overrepresented in prison, insane asylums, and poorhouse populations. Large-scale...