LET’S TRY an outrageous generalisation, prompted by the appearance of Sebastian Barry’s mesmerising On Canaan’s Side on the longlist for the Booker Prize. It can be contradicted by a thousand qualifications and counter-examples, but it is nonetheless worth positing. It is this: that the great theme of the contemporary Irish novel is not Ireland but the US.

America has long been a presence in Irish writing, of course. A few nights ago, I brought some young American cousins to the Abbey to see Translations, a play I’ve watched dozens of times. Its frame of reference is literally Anglo-Irish, setting a version of Irishness against a version of Englishness. Yet, watching it with the young Americans, it struck me more forcibly than ever before how, even here, the US looms over everything as the third force that challenges and subverts the play’s big duality. It insinuates itself under the play’s skin. Even when writing about Ireland and England, in other words, a searching writer like Friel can’t avoid the great presence that hovers beyond the western horizon.

But even in this context, there is something especially striking about the sheer extent to which so much that is interesting in contemporary Irish fiction is set in the US. At the risk of qualifying one sweeping generalisation with another, one might suggest the phenomenon is particular to the generation of male novelists aged 45 to 60. It is not important to an older writer like John Banville or a younger one like Paul Murray, or to a female novelist like Anne Enright. (Enright, admittedly, has her own New World in Eliza Lynch’s Paraguay.) Yet any list of the most powerful Irish novels of the last few years would surely include Joseph O’Connor’s Redemption Falls, Colm Toibín’s The Master and Brooklyn, Colum McCann’s This Side of Brightness and Let the Great World Spin, Joseph O’Neill’s Netherland, Roddy Doyle’s Oh, Play That Thing. And now, Barry’s On Canaan’s Side. Each is set, in whole or in significant part, in the US.

It is perhaps even more striking if you look at it from the other side of the Atlantic. Suppose you were an American and were asked to name the two most potent fictional responses to the national trauma of 9/11. There’s a good chance that you’d come up with Netherland and Let the Great World Spin. Neither, it is true, is merely a 9/11 novel, still less a direct description of those terrible events. But each feels like a necessary story for the US, post-9/11, with McCann celebrating and mourning what has been lost and O’Neill imagining a post-imperial New York. This is, surely, a remarkable thing.

The sense, then, is not just that a generation of Irish male novelists needs the US but also that the US needs them. The large sales of, and critical acclaim for, most of these books in the US suggest that these Irish writers are not merely inventing their own America but touching some kind of nerve in the one that actually exists.

But if the US really is the great theme of so much contemporary Irish fiction, why should this be so? At one level, the phenomenon makes little sociological sense. If we go back, for example, to Friel, the inescapable presence of America has obvious roots in lived reality: emigration to the States is an overwhelming fact of the lives of Friel’s Gar O’Donnells and Cass Maguires. But the odd thing is that this is not true in general for the Ireland from which the more recent writers have come. If anything, the opposite was the case: the era in which the novels in question appeared was one in which forced emigration from Ireland had all but ceased.

One could push this a little further, however, and say that there is nevertheless a real Irish experience behind at least some of the novels. The most interesting thing that was happening in Ireland at the cultural level over the last 20 years was mass immigration. But it was an experience from which, by definition, native Irish writers were imaginatively excluded. One way of responding to this has been to reclaim the Irish experience of being an immigrant in a strange country. That strange country couldn’t be the contemporary US: when Irish people were doing their Christmas shopping in Macy’s, it was hardly credible to posit today’s New York as an alien planet.

Hence the decision to reach back to the 19th century, the 1920s or the 1950s. That this is more than creative happenstance is suggested by the broad similarity (admittedly on the surface only) of Brooklyn and On Canaan’s Side.

But there are other reasons. One of them is surely a parallel with Irish writers setting so much of their work in England in the 19th century - the sense that the apparent imperial power is where it’s at, the desire to be close to the centre of things. Another, more negative, reason is the relief from having to try and make sense of the confusing, vulgar, rapidly shifting Ireland of the last 20 years. America, with its infinite tolerance for personal reinventions, is by comparison uncomplicated. The great theme of the American immigrant novel - starting from scratch and making yourself up - is handy when you’re looking to escape from the infuriating entanglements of boom-time Ireland.

But if this were all there were to it, most of this work would not be potent. What makes it so is a consistent sense of mourning. When Barry’s Lilly Beere is approaching the coast off New Haven, she gets the smell of America, the scent of a strange nostalgia: “Even before we got there, I was experiencing a sort of nostalgia for the land, I do not know how other to describe it. As if I had been there before, had left it, and was returning after a long voyage.”

And that sense of nostalgia for the unknown country pervades these novels, as if there is a special Irish mourning for the sense of a mystery and wonder that America once contained. As if Ireland, having dreamed the American Dream with a peculiar intensity, is grieving for its loss.