Proof of God: The Bible
Proof of Middle Earth: The Lord of the Rings trilogy, The Hobbit, The Silmarillion...
By the standard of "Evidence" that Christians claim to prove the existence of God, there is More Evidence of Middle Earth, Hobbits, Wizards, Dragons, and Elves than there is of God and Heaven.
Get real, Christians. Harry Potter isn't real because he has 7 books about him. Neither is God.
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But Tolkien never claimed his work was anything more than a work of fiction (although his original concept of Middle Earth was based in England in roughly 6000 BC).