What Tolkien was largely dismissing is the notion that his world was a direct allegory. He readily acknowledges that the comraderie and sacrifice he experienced in the trenches of WWI manifests itself in Frodo and his companions, as well as the doomed but defiant determination of the people of England/Gondor in the face of assured destruction, etc. So there are themes that bind the two worlds but he was adamantntly dismissive of any direct mappings (ie Germany as Mordoe or whatever).

Really LotR is about mortality and power.