When the United States offered Ireland the opportunity to join the European Recovery Plan (ERP) after World War II, Irish officials and leaders had a unique opportunity to move beyond Ireland's conservative political and economic isolation and, with ERP resources, to work towards European integration. However, extreme nationalism and the issue of the partition of Northern Ireland impeded even the most forward thinking Irish leaders of the time, like Seán MacBride, from fully realizing the opportunity of ERP because these leaders hijacked Marshall Plan propaganda for the purpose of promoting their own political, nationalistic agenda. Even strong proponents of European recovery and European integration, like the Irish intellectual Sean O'Faolain, were not immune to the pull of Irish nationalism. O'Faolain's 1951 Marshall Plan film The Promise of Barty O'Brien provides an historical and cultural lens into Ireland's struggle between modernization and extreme Irish nationalism, which was often isolationist and fervently against the partition of Northern Ireland. Despite O'Faolain's support of ERP, modernization, and integration, the film demonstrates a glorification of Ireland's agrarian and revolutionary past. Extreme Irish nationalism, the failure to break economic ties to the United Kingdom, and demands that anti-partition be a condition of membership in NATO alienated both U.S. and European officials. This thesis will expand and contribute to the existing scholarship on the ERP and Irish nationalism in the post World War II era because of the analysis of diplomatic affairs in connection with unique and significant Marshall Plan films like The Promise of Barty O'Brien.