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
Baum wrote "The Wonderful Wizard of Oz" without any thought of a sequel. After reading the novel, thousands of children wrote letters to him, requesting that he craft another story about Oz. In 1904, he wrote and published the first sequel, "The Marvelous Land of Oz", explaining that he grudgingly wrote the sequel to address the popular demand. Baum also wrote sequels in 1907, 1908, and 1909. In his 1911 "The Emerald City of Oz", he wrote that he could not continue writing sequels because Ozland had lost contact with the rest of the world. The children refused to accept this story, so Baum, in 1913 and every year thereafter until his death in May 1919, wrote an "Oz" book, ultimately writing 13 sequels. The "Chicago Tribune"s Russell MacFall wrote that Baum explained the purpose of his novels in a note he penned to his sister, Mary Louise Brewster, in a copy of "Mother Goose in Prose" (1897), his first book. He wrote, "To please a child is a sweet and a lovely thing that warms one's heart and brings its own reward." After Baum's death in 1919, Baum's publishers delegated the creation of more sequels to Ruth Plumly Thompson who wrote 21. An original "Oz" book was published every Christmas between 1913 and 1942. By 1956, five million copies of the "Oz" books had been published in the English language, while hundreds of thousands had been published in eight foreign languages.