WW2: Why was the Ardennes regarded as impassible via tanks by the Allies, yet the Germans seemed to roll right through? Why did the French pay it so little mind that Germans were able to flank them?
While more can certainly be said, I've answered almost this exact question before here (by me /u/superplaner, I see you automoderator). If you have follow-up questions I'd be happy to help to the best of my ability.