Rinkitink in Oz

Pingaree is an island in the Nonestic Ocean that surrounds the fairy countries that encircle the Deadly Desert that surrounds the Land of Oz. Many years before this story begins, the armies of Regos and Coregos sought to invade Pingaree, but their advance was repelled by Pingaree's king with the help of three magic pearls given to him by the Mermaids. The Blue Pearl gave the king superhuman strength, the Pink Pearl protected him from any form of harm, and the White Pearl provided words of wisdom that only he could hear. Buoyed by the Pearl's magic powers, the king of Pingaree led his people to victory and the invaders from Regos and Coregos drowned on the return trip. Wikipedia