Andorra is one of the very few countries on Earth that no one has ever bothered invading. True, Hannibal passed through with his elephants, but he had the Roman Empire to destroy and didn't stay long. Napoleon once planned to annex it, but the Andorran delegation to Paris decided not to go to the talks. Napoleon's clerks forgot about them.
And then so did Napoleon.
The Nazis thought about it briefly in 1943, but the Andorran leaders petitioned Spanish dictator Generalissimo Franco to intercede on their behalf. Surprisingly, he remembered to do so. And the Nazis said, "What? Where? Andorra? Can you spell that again? OK. We weren't that interested anyway; had problems finding it on the map." Or words to that effect.