The historian, Nicholas Mansergh, writing in 1965, was of the view that American aid to Ireland's independence struggle was not ‘decisive’. Now, however, it is widely accepted in the scholarly and popular literature that it is impossible to imagine Irish independence without the aid of Irish America. Francis Carroll, having examined the archival record, news media and the ever-growing secondary literature, over many decades, supports this consensus arguing that the United States ‘played a dynamic part in Ireland's emergence as an independent state’ (p. xii). Of course, this ground has been covered in numerous books and articles. In the 1950s, Charles Tansil in his study of Irish-American relations of this period, made a polemical attack on Woodrow Wilson for his pro-British bias and suggested the electoral disaster which his Democratic Party suffered in 1920 was down to an angry Irish-America. Since then, more measured tomes, notably those by Alan J. Ward (1969) and Bernadette Whelan (2015), have emerged. Professor Carroll wrote in the 1970s on American public opinion and the Irish question during the independence struggle and earlier versions of some of the chapters here have appeared as scholarly articles.

The author makes a detailed, if somewhat familiar, case for the importance of America to Irish freedom in the period between 1916 and 1928. He asserts that Irish America, disillusioned by the slow progress of home rule, the apparent success of Ulster's militant opposition and John Redmond's support for the British war effort had broken with the Irish Parliamentary Party by 1915. The path was open to the militants exemplified by John Devoy and the previously fringe Clan na Gael to win the hearts and minds of Irish America and be a lynchpin of the Easter Rising. The Clan were able to supply $100,000 to the Irish Republican Brotherhood and the Irish Volunteers prior to 1916. Five of the seven signatories of the proclamation had spent time in the United States (though it is not made clear whether this radicalised them). American public opinion, including some of the Irish there, was initially critical of the Rising, as a betrayal of Redmond. As in Ireland, however, the executions of the leaders swung opinion 180 degrees. But Irish opposition to entering the war and the anti-Wilson attitude of more militant Irish Americans alienated major political figures, including the re-elected president and Theodore Roosevelt, who were both sympathetic to Ireland. Nonetheless, Wilson and other senior American officials pressed Britain to take a more constructive line over Irish self-rule.

Efforts by the British government during 1917 to resolve the Irish question, including the 1917 Irish Convention, arguably were driven by the need to remove the grit of Ireland from the smooth running of the war time alliance. But, crucially, advice on conscription was ignored, showing there were limitations to American influence. Carroll argues, as have others, that the ignoring of the American Commission on Irish Independence by Britain and the United States turned Irish-American opinion against both Wilson and the Versailles Treaty. One of Wilson's advisers would later claim it was the failure to solve the Irish question that more ‘than anything else … was responsible for the Treaty's rejection’ (p. 62). Later in 1920–21, the American Commission on Conditions in Ireland by exposing ‘the cruel and inexcusable actions' of the British in Ireland ‘made a significant contribution to ending the Anglo-Irish War’ (p. 110), as did the work of the American Committee for Relief in Ireland which ‘significantly influenced the British government's decision to open talks with the Irish’ (p. 140).

Money raised in the United States was also the key source of funds that kept the Sinn Féin movement alive. By happy coincidence for the Irish cause, Anglo-American tensions over Britain's alliance with Japan in 1921 provoked President Harding's secretary of state, Charles Hughes to warn British diplomats that Anglophobic elements in the U.S. Congress would use the issue to debate a resolution supporting an Irish republic. This certainly caused some anxiety in British government circles. The remainder of the book focuses on the relationship between the Irish Free State and the United States in the 1920s. There is an examination of how the Free State became the first British dominion to have reciprocal diplomatic relations with the United States, as well as accounts of W. T. Cosgrave's visit to America in 1928 and the return visit to Ireland of Secretary of State, Frank Kellogg, the same year. These developments, it is asserted, were vital in the forging of the international identity of the new Irish Free State.

The book is readable, lucid and, in the main, persuasive. It is also well presented with twelve contemporary photographs reproduced. This reader would take slight issue with the somewhat monolithic view of the 20 million Irish Americans. Also, in view of the considerable amount of writing that has appeared on this subject, it would have been useful if the author had been more explicit in explaining what lacuna he was trying to fill and had engaged more with the historiography in the text. Nonetheless, Professor Carroll has given us a very useful synthesis of his decades of study of America and Ireland in the revolutionary period that will be of interest to students and scholars of Irish America, U.S.-Irish relations and ethnic politics in the United States in the first quarter of the twentieth century.