Colin Barr's study focuses mainly on the appointments of Irish bishops in six different areas of the world within the Roman Catholic Church between 1829 and 1914. From the United States, to Newfoundland, to Canada, to South Africa, to Australia and New Zealand, Barr charts the movements and key events, often dealing with the circumstances surrounding these appointments. Beyond the focus on the Hibernian aspects of the Church, Barr attempts to show that there was a method to all of these nominations. Conceived of and facilitated by Paul Cullen, Ireland's first cardinal, this global network of Irish bishops coalesced itself into something grander – an Irish empire.

Undergirding Barr's storyline is one of the most impressive hauls of documentary evidence one will likely find within a single monograph. More than a hundred archives spanning several continents are employed. This is remarkable by any measure and that he was able to come to grips with the multiple storylines within each of the chapter settings is no small feat. He is to be commended for carrying out such an ambitious project. To this extent, the book's greatest contributions are in filling in all of the interesting promotion vignettes, for he employed numerous original sources.

But because this book contains so many micro-narratives spread across the globe, Barr struggles to tie these into anything more substantive and produces a very thin history that omits important context. Additionally, the work is void of any sound methodology or scientific rigour related to identity, relying haphazardly on personal missives to conclude that those comprising ‘Ireland's empire’ were half-Irish, half-Roman.

Barr leans heavily on Paul Cullen's relationship with Propaganda Fide, which acted as the catalyst for Cullen's religious heist. It is true that Propaganda Fide was one of the most important congregations of the Roman Curia. But Barr's understanding of it is over-simplistic, perhaps due to his lack of Italian (no Italian secondary sources are employed): ‘If the key to the church was Propaganda, the key to the Propaganda was the cardinal prefect’(p. 9). But cardinal prefects were overworked, juggling a half-dozen different responsibilities. They often relied upon their consultants and the congregation's secretary. What is more, the administrative practices in Rome, some of Europe's most backward, were nothing if not disorderly; Barr unwittingly underscores this point when he draws attention to the unqualified Italian priest, Enrico Carfagnini, who was elected bishop of Habour Grace, Newfoundland, on the basis of a single, biased letter from a little known diocesan priest (p.102).

There was another problem related to Cullen and Propaganda Fide. Cullen was never officially part of Propaganda Fide after 1832, devoting himself full-time to heading the Irish College (r. 1832–50); not only does Barr never tell us this fact, he never explains how someone outside the congregation would have had a monopoly over it, where English-speaking areas were concerned. Barr is content to rest his thesis on three quotations related to Pope Gregory xvi, for example that Cullen has ‘intimate access [to the pope]’ (p. 11). But the pope was not part of Propaganda Fide in its day-to-day activities; and having access to the pope did not guarantee influence at Propaganda Fide.

More troubling is Barr's failure even to discuss how this twenty-something-year-old (in 1829) would have had more pull in the Catholic Church in the lands of the British Empire, as is implied in his main thesis, when there were more senior English clerics in Rome. The future Cardinal Nicholas Wiseman was rector of the much larger and more important English College, at the time Cullen headed the smaller Irish College; and Wiseman was also named cardinal fifteen years ahead of Cullen despite being nearly the same age. The English cardinals Thomas Weld and Charles Acton were also active in Rome during these years and held very large sway. What is more, there is no discussion of the evolution of the role of college rector into agent and curial advisor, so readers are somewhat confused how as to how a college rector with full-time duties would have time to construct a global empire. A careful reading of the work's sections dealing with appointments prior to 1850 reveals Cullen mainly on the sidelines and barely visible.

Finally, Propaganda Fide was not the only organisation to send out missionaries. The Society for the Propagation of the Faith was founded in 1822 in Lyons, to fund such endeavours. The society possessed something that neither Propaganda Fide nor Cullen nor his Irish co-religionists had much of – money. There can be no serious discussion of empire without a discussion of finances. No overseas appointments and no new constructions could take place without the necessary funds. Barr appears unaware of this fact, though numerous references to finances find their way into the work's micro-histories. ‘Money was also a problem’ (p.59); ‘The Propaganda had none to spare’ (p. 62). In fact, during Pope Gregory xvi's papacy alone, a half-dozen emergency loans from the Rothschild banking house were needed to avoid insolvency.

Barr's assessment of the ethnic admixture of these men comprising the empire lacks any scientific approach. Rather than explaining at the outset how he intends to measure Hiberno-Roman identity, which is an enduring theme of the work, he proceeds on an ad hoc basis, from personal correspondence, shifting the boundaries of the argument when convenient to fit the contrived thesis. In the chapter on the United States, Barr draws distinctions between Irish-born and American-born clerics, intimating that this is the yardstick by which Hiberno-Roman identity will be assessed. So focused at times is Barr on maintaining the Irish part of the ‘empire’, that some of the conclusions are just plain odd. He referred to the death of the American-born bishop, Samuel Eccleston, as an ‘Irish victory’ (p. 67). The problems in Philadelphia were exacerbated because one of the bishops at the Baltimore conference, Henry Conwell, ‘downplay[ed] his own Irishness’ (p. 28). And, bizarrely, he suggests that the economic conditions of Irish Catholics in Boston ‘lagged far behind their brethren elsewhere in the United States’ because the bishops in that city were born in the US and not Ireland, and that conditions improved once Irish-born prelates arrived (p. 26).

Barr's Hiberno-Roman identity discounts British or local influences. Scores of scholars in neighbouring academic fields have observed ‘fresh colonial identities’ as ‘complex and multi-layered, contingent on a whole variety of experiences’, experiences that Barr discounts. Evidence within the book itself even suggests that the issue is more complex: ‘The Irish … are easily amalgamated with the Americans – their principles, their dispositions, their politics, their notions of government, their language, & their appearances become American very quickly’ (p. 40) and later, ‘the Catholics of New York were “principally Irish and American in feeling”’(p. 41). Michael Howley held ‘four distinct identities with no difficulty’ according to Barr: ‘Catholic, Irish, Newfoundlander, and citizen of Britania’ (p. 111).

The book's conclusion is the perhaps the most perplexing chapter: Cullen is barely mentioned, despite being the book's protagonist, while a lot of space is given to the issues of mixed marriage, education and alcohol. Illustrating once again the book's lack of context outside the Hibernian realm, Barr claims that the Irish led the way in championing the Church's opposition to mixed marriage: ‘when it came to [mixed] marriage policy, Rome followed where Ireland led’ (p. 470). He then walks back this claim two pages later when listing the notable exceptions. And he appears unfamiliar with the well-known Cologne affair of the late 1830s and the trouble that the archbishop of Poznan and Gniezno also found himself in; both men endured persecution, imprisonment or exile defending this very issue.