JRR Tolkien found many occasions to explain that Middle-earth is simply our world, and that the stories are set in an imaginary past time for our world.
D. Gerrolt: I thought that conceivably Midgard might be Middle- earth or have some connection?
J.R.R. Tolkien: Oh yes, they're the same word. Most people have made this mistake of thinking Middle-earth is a particular kind of earth or is another planet of the science fiction sort but it's just an old-fashioned word for this world we live in, as imagined surrounded by the Ocean.
D. Gerrolt: It seemed to me that Middle-earth was in a sense, as you say, this world we live in, but this world we live in at a different era.
J.R.R. Tolkien: No ... at a different stage of imagination... yes.
here is what else the author said in his letters:
Middle-earth is just archaic English for οικουμένη, the inhabited world of men. It lay then as it does. In fact just as it does, round and inescapable, —Tolkien Letter 151
Middle-earth’, by the way, is not a name of a never-never land without relation to the world we live in (like the Mercury of Eddison). It is just a use of Middle English middel-erde (or erthe), altered from Old English Middangeard: the name for the inhabited lands of Men ‘between the seas’. And though I have not attempted to relate the shape of the mountains and land-masses to what geologists may say or surmise about the nearer past, imaginatively this ‘history’ is supposed to take place in a period of the actual Old World of this planet — Tolkien Letter 165
I am historically minded. Middle-earth is not an imaginary world. The name is the modern form (appearing in the 13th century and still in use) of midden-erd > middel-erd, an ancient name for the oikoumenē, the abiding place of Men, the objectively real world, in use specifically opposed to imaginary worlds (as Fairyland) or unseen worlds (as Heaven or Hell). The theatre of my tale is this earth, the one in which we now live, but the historical period is imaginary. The essentials of that abiding place are all there (at any rate for inhabitants of N.W. Europe), so naturally it feels familiar, even if a little glorified by the enchantment of distance in time. Tolkien Letter 183
D. Gerrolt: I thought that conceivably Midgard might be Middle- earth or have some connection?
J.R.R. Tolkien: Oh yes, they're the same word. Most people have made this mistake of thinking Middle-earth is a particular kind of earth or is another planet of the science fiction sort but it's just an old-fashioned word for this world we live in, as imagined surrounded by the Ocean.
D. Gerrolt: It seemed to me that Middle-earth was in a sense, as you say, this world we live in, but this world we live in at a different era.
J.R.R. Tolkien: No ... at a different stage of imagination... yes.
here is what else the author said in his letters:
Middle-earth is just archaic English for οικουμένη, the inhabited world of men. It lay then as it does. In fact just as it does, round and inescapable, —Tolkien Letter 151
Middle-earth’, by the way, is not a name of a never-never land without relation to the world we live in (like the Mercury of Eddison). It is just a use of Middle English middel-erde (or erthe), altered from Old English Middangeard: the name for the inhabited lands of Men ‘between the seas’. And though I have not attempted to relate the shape of the mountains and land-masses to what geologists may say or surmise about the nearer past, imaginatively this ‘history’ is supposed to take place in a period of the actual Old World of this planet — Tolkien Letter 165
I am historically minded. Middle-earth is not an imaginary world. The name is the modern form (appearing in the 13th century and still in use) of midden-erd > middel-erd, an ancient name for the oikoumenē, the abiding place of Men, the objectively real world, in use specifically opposed to imaginary worlds (as Fairyland) or unseen worlds (as Heaven or Hell). The theatre of my tale is this earth, the one in which we now live, but the historical period is imaginary. The essentials of that abiding place are all there (at any rate for inhabitants of N.W. Europe), so naturally it feels familiar, even if a little glorified by the enchantment of distance in time. Tolkien Letter 183