The Shaping of Middle-Earth

The depth of lore is incredible, and I wonder what sparked Tolkien's creative process for building this universe from scratch.

I loved the richness, but at times it was a lot to take in—was that intentional to immerse readers or just Tolkien's thoroughness?

His expertise in philology and history clearly shaped Middle-Earth. I'm curious how much of that was deliberate world-building versus natural passion.