The story of the massive Irish immigration to North America between 1820 and 1924 has its roots in the nature of the relationship between Ireland and Great Britain after 1800, when the Act of Union, creating the United Kingdom, was instituted by the English Parliament and ratified by an almost entirely bought-off Irish Parliament ("Act"). The Union, as far as Ireland was concerned, was rescinded in 1922, by the Anglo-Irish Treaty, which created the Irish Free State and which reserved Ulster Province, or Northern Ireland, for the UK (Boland and Ranelagh). The years between the two treaties were marked by almost unrelieved contentiousness over the status of the Irish. The Act of Union, designed to assert the legality of British supremacy forever, had the effect of causing Catholics to agitate for "Irish civic and religious freedom and for separation from Great Britain" ("Ireland" 414). For some 30 years, a series of armed revolts occurred, but by 1829, Irish Catholics were allowed religious freedom and ultimately to sit in Parliament. By 1886, a bill calling for Irish home rule had been introduced, but it was defeated by British and Irish Protestant opposition.
Irish people had migrated from Ireland to America before the Revolutionary war, often as indentured servants (Lennon). Crevecoeur's 1770 description of Americans as a "promiscuous new breed" comprising "English, Scotch, Irish, French, Dutch, Germans, and Swedes" positions the Irish as an integral part of the growing population of the New World. An Irish Brigade led by regiments affiliated with Lafayette during the American Revolution reportedly "demanded the right o be the first o the French service to strike Britain on American soil" (MacManus 482).
Over the course of the 19th century, massive numbers of Irish, mainly Catholics, left Ireland permanently. The momentum for the migration began in the mid-1840s, when Ireland's staple potato crop failed three years in a row. The...