Assel, I’ve never heard of the “Berlin depository” so I can’t help with that. The U.S. Copyright office registers copyright for books published in the U.S. Here’s a link that explains their function: .
16.-1. The penalties imposed by this act relate, first, to the violation of the copyright of books secondly, the violation of the copyright of prints, outs or engravings, maps, charts, or musical compositions thirdly, the printing or publishing of any manuscripts without the consent of the author or legal proprietor; fourthly, for inserting in any book, &c., that the copyright has been secured contrary to truth.
The name says it all—copyright is the right to copy a work. Copyright prevents bookstores from buying one book from the author, making copies and then selling them to its customers. The customers are not just buying the book; they are buying the author’s intellectual property: the story, the characters and the setting.