Tolkein apparently furiously denied allegory - although there are preexisting tropes that predate even his influence (decline of the mythic past Götterdämmerungn Atlantis) is hard to not see. Which I suppose probably owes itself both to decline of youthful myths like "parents and ancestors as infalliable" and the distant mutated memories of the Bronze Age collapse where the greatest empires indeed did fall from lofty heights and take millenia to be reached again.
What I'm pointing to isn't allegory though. Allegory would be if the Rohirrim at Helms Deep represented the Belgians and the elves led by Haldir represented the British Expeditionary Force. They don't.
But stories are still about (among other things) the choices people make, the way we see those choices, and the things we think about our own choices.
He denied allegory with WW2 in the foreword to Lord of the Rings. It's nearly impossible that his own service in WW1 with its industrial warfare had no influence on his writing. Mordor bears a striking resemblance to the trench-infested battlefields of Europe.
