Philip Roth, one of the most prominent living writers in the US, during an interview concerning his book Indignation, was asked what he thought about this. He answered (I'm translating Philip Roth back to English once that his words were translated into Italian in this article published in La Repubblica):
"It is such a ridiculous polemic that I can't even understand it. I think that American literature, from after the Second World War until now, has been the most important of the world, with authors like Faulkner, Hemingway and Bellow. And also nowadays we have top notch writers such as Don DeLillo, E. L. Doctorow, Cynthia Ozick, Joyce Carol Oates and Toni Morrison. I feel that I am in the company of excellent colleagues".
Take that Mr Engdahl!
But of course Mr Roth is himself an "isolated, insular" American, what does he know about world literature? :-P