Copyright status of The Wizard of Oz and related works in the United States
"The Wonderful Wizard of Oz" was published in 1900, and was the first to enter the public domain in "1956". This allowed Reilly & Lee, the publisher of all the other Oz books (as well as Baum's other books) to issue their own edition of "The Wizard of Oz", which had previously been published by George M. Hill Company and later by the Bobbs Merill Company after Hill went bankrupt..
The Wonderful Wizard of Oz
Some critics have suggested that Baum may have been inspired by Australia, a relatively new country at the time of the book's original publication. Australia is often colloquially spelled or referred to as "Oz". Furthermore, in "Ozma of Oz" (1907), Dorothy gets back to Oz as the result of a storm at sea while she and Uncle Henry are traveling by ship to Australia. Like Australia, Oz is an island continent somewhere to the west of California with inhabited regions bordering on a great desert. One might imagine that Baum intended Oz to be Australia, or perhaps a magical land in the center of the great Australian desert.