The Shire, a pastoral Garden of Eden kept in a medieval-communal state where the biggest worry is how much food your friend is going to eat when they come for a visit to get high and drunk.

Mordor, an advanced state using all kinds of witchery like gunpowder and mechanical engineering, looks like hell filled with ash and dust like a factory might.

i wonder what he meant by this

Tolkien specifically stated that it wasn’t an allegory because his bff CS Lewis (whose Narnia books were explicitly supposed to be read as christian allegory with Alan = Jesus) tried to pressure him to do the same. Tolkien was Catholic and Lewis was Protestant, but they were both very religious. Tolkien felt that the approach Lewis took was too ham-fisted.

However, what Tolkien specifically objected to was the interpretation of his work as allegorical to the world wars. He would go on and on about how the ring was not the atomic bomb. He was, however, an unapologetic romanticist and he made sure his readers knew that. Saruman was the bad guy in that respect - he served evil out of greed and cut down forests and destroyed the land to serve his own ambition, the allegory with which he’s bashing readers over the head in the last bit with the Scouring of the Shire. He really liked the idea of jolly peasant farmers, the reality of actual peasant farmers not being relevant.

I think his work was colored by his war experiences, but wasn’t intended as allegorical in that respect. On the other hand, hobbits, Treebeard, Tom Bombadil, Lothlorien, and the rest were very deliberate.