This dissertation examines the development of the ideal of the United States as a"Nation of Immigrants," from the early twentieth century until the passage of the 1965 Immigration and Nationality Services Act, with a focus on the central role of the history of Irish immigration to the United States in this process. In the wake of the great wave of immigration in the late nineteenth and early twentieth century, Irish-American political activists embraced their identification as a patriotic and respectable "old immigrant" group, in comparison with more problematic recent arrivals from Southern and Eastern Europe. Irish-American campaigners and journalists pointed to thecontributions of the Irish to American civic society as a demonstration of Ireland's preparedness for self-government and independence from Great Britain. Éamon de Valera's fundraising and speaking tour of the United States between 1919 – 1920 on behalf of the Republic of Ireland reflected the compatibility between Irish anti-colonial republicanism and the Wilsonian embrace of national self-determination after World War I. However, changes to United States immigration policy – in particular, the national origins quota system within the 1924 Immigration and Nationality Act challenged many of the assumptions amongst the Irish about the legitimacy and recognition they sought for Irish-American ethnic nationalism in the United States. As the once-robust Irish-American political network disintegrated, many historians, scholars and policymakers argued that emigration threatened Ireland's national survival.After World War II, the history of Irish immigration to the United States was adopted as a usable past by historians, politicians and ordinary citizens who campaigned for radical changes to American immigration policy in response to the migration crisis of post-war Europe. Historian Oscar Handlin's work of the "uprooted" immigrants from nineteenth-century Ireland provided compelling narratives of historic precedents for American liberal politicians such as Herbert Lehman and John F. Kennedy. Lehman, Kennedy and their colleagues campaigned on behalf of their immigrant constituents for comprehensive rights-based legislative reforms related to displaced persons, family reunification and the elimination of the national origins quota system. This dissertation argues that this popular movement culminated in the radical changes to United States immigration policy within the 1965 Immigration and Nationality Services Act.