Complex sentence: Ozma uses the magic belt to send them all home, and to forestall a future invasion of Oz, Glinda uses a magic charm to render Oz invisible and unreachable to everyone except those within the land itself.
Split into simpler sentences: Ozma uses the magic belt to send them all home. To forestall a future invasion of Oz, Glinda uses a magic charm to render Oz invisible and unreachable to everyone except those within the land itself.