One of the characteristics of American literature in the period from 1800 up to 1950 or so is its individualistic heroes, often lacking a past and being somewhat estranged from society. Hence the sum total of Moby Dick's protagonist's backstory is "Call me Ishmael"; think also of Edgar Allan Poe's many isolated, rootless viewpoint characters, or Huckleberry Finn, the "poor motherless thing". It's not just a feature of American letters during the period, of course (Lord Jim, which I happen to be reading at the moment, is an obvious example), but it is a notable one.
This is in contrast with European novels of the same period, which tended to have large casts of characters with obsessively detailed backgrounds and complicated familial relationships - a good example being Emile Zola's "Rougon-Macquart" novels: twenty books about the history of two branches of an extended family during the Second French Empire. This, of course, harks back to a much older tradition: medieval and pre-medieval authors thought it of the greatest importance to locate their heroes in a family tree, and often go to some length to detail what so-and-so's father and grandfather and great-grandfather did before the proper story gets going.
(One doesn't need to be Sigmund Freud to observe that the former of these bodies of literature was mostly written by the children and grandchildren and great-grandchildren of immigrants to a newly discovered continent with a so-called "frontier" and the latter was written by people whose ancestors had lived since time immemorial in densely populated landscapes with very conservative social mores.)
Tolkien sits interestingly between these two positions. On the one hand, his two heroes (which I still take to be Bilbo and Frodo even though a case can be made that Sam is really the chief protagonist of LotR) are given lengthy and detailed backgrounds, and it is even made clear that their ancestry and bloodlines have had a strong influence on the formation of their character. They are by no means "William Wilsons". And Tolkien was clearly deliberately channeling older forms of literature in this regard.
And yet The Hobbit and The Lord of the Rings also explore very "American" themes: the leaving of home to make a new life elsewhere; the exploring of a vast and dangerous land in the name of adventure; the severing of familial ties (neither Bilbo nor Frodo appears to actually care about his relatives); the sense of estrangement from society (again, neither of them is exactly an integral part of their community even at the beginning of their respective stories). Neither of the ring-bearers is Bartleby the Scrivener. But nor are they like characters from a Jane Austen novel; they are escaping society, not finding their way in it.
Part of the success of Tolkien's work can therefore be attributed, I think, to his straddling two quite distinctive pre-modernist approaches to literature - the American and the European. He was very interested in the details of his world. But his characters are not embedded in them.