Witches have pet dragons. Dragons go out and burn up kingsdoms to get riches and gold for their beds.

OBVIOUSLY the wicked witch of the west was sneaking into her dragon's lair to steal bits of his bed to pay off her soldiers and buy the flying monkeys.

That's why Dorothy got away with everything and the witch had to throw her own fireballs at scarecrow. The dragon found out and left her (They weren't married so no lawyers were really necessary). He took his riches with him, and then the witch, underfunded, had to go understaffed, which is why Dorothy and her crew were able to sneak into the castle. Also, thet's the real reason why the soldiers were so pissed at the witch in the end.

Little did anybody know, that dragon was the one who funded the building of the yellowbrick road. Sort of a spiteful thing to get back at his thieving former lover.
The poor sap never realized that he was only a pet to her.