The melody for "For He's a Jolly Good Fellow" was an older French song, "Malbrough s'en va en guerre", about the rumored, but ultimately only rumored, death of Churchill's ancestor, whom apparently the French disliked.
Perhaps the French thought up the new lyrics just to get everyone in England and America to sing it. Which would be pure Gallic genius. The divine anointing oils of the first court of Europe did some fine work there.