1840–1860 – A large influx of immigrants, mostly from western and northern Europe, come to the United States. For example, during five years of this period, almost 500,000 Irish move to the United States, escaping a devastating potato famine in Ireland in 1845. Between 1820 and 1860, the Irish constitute more than one-third of all immigrants to the United States, many of them settling in Boston, where bronze statues have been dedicated in their memory. (Library of Congress)