The Mongols made such a tremendous impression because they mass murdered anyone who got in their way. They easily brushed aside the armored knights of Europe. They would have made it all the way to Portugal except for the fact that Ghengis Khan died and they were called back to Mongolia to decide on a new leader.
Tolkien famously hated allegory. He had a rant that was basically, “Does every book have to be a fucking allegory? Why can’t I tell a story and it’s just a story? Jesus, people.”