The Italian American population numbers more than fourteen million through the fourth generation. The largest wave of immigrants (around four million) arrived in the United States at the end of the nineteenth and start of the twentieth century.

The majority hailed from the largely overpopulated and poor central and southern parts of Italy, where the populace had been impoverished by centuries of foreign misrule, natural disasters and political unrest. They settled in major urban centers like New York, Chicago, Boston and San Francisco.

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Source: http://www.loc.gov/