You probably only know of the two Wicked Witches and the one Good Witch from the classic film, and maybe you know Mombee from the later sequel, but the books are full of spellcasters, sorcerers, and other practitioners of magic.
Ding Dong was especially proud, powerful, and dangerous.
The few who knew of her existence knew not to mention her, let alone insult her.
Munchkins are as ignorant as they are small, so they didn’t realize their mistake of singing “Ding Dong, the witch is dead!”
“No,” a voice muttered. “You’re dead.”
A massive firestorm wiped Munchkinland from the map.