The United States census of 1910 revealed that there were four and a half million people in the United States who had beenborn in Ireland, or who had at least one Irish-born parent. The figures did not reveal that many other Americans identified themselves with Ireland, the country of their grandparents, or even of their great-grandparents, and it was not unusual for Irish-American leaders at that time to claim the support of fifteen or twenty million fellow Irish-Americans. A great many of these had, indeed, managed to retain a sense of Irish identity and this was in part because they, or their forebears, had largely settled together in Irish ghettos in large cities. In addition they had been forced inwards to their Irish community for support when persecuted by the ‘ Know-nothings ’ and other nativist groups in the nineteenth century. This Irish subculture in which they lived was cultivated by three groups of fellow Irish-Americans who had an interest in promoting an Irish-American community, the better to control and command the Irish-Americans themselves; the Roman Catholic Church, which was very much an Irish Catholic Church in America, the Irish political bosses, interested in political power rather than Ireland, who had risen to power in the Democratic party by their ability to control the Irish vote, and a third group which utilized the audience they both nurtured, the Irish nationalists. The skill with which these nationalists mobilized Irish-Americans in support of Ireland’s claim to independence added an important dimension to the British government’s Irish problem for it became a problem for successive American governments too. As long as Ireland remained tied to England there were in America men and women prepared to emulate John Mitchel who had declared, when he first landed in New York in November 1853, that he intended to make use of the freedom guaranteed him in America to stimulate the movement for Irish independence. It is the object of this paper to review, albeit briefly and incompletely, the significance of the activities of these Irish-American nationalists in the struggle for Irish freedom and in the development of Anglo-American relations during the period from the Boer war, which began in October 1899, to the Anglo-Irish treaty of December 1921.