A more thorough explanation:

The manufacturing clause is a part of the Copyright Act that limits the importation of certain works. There are two versions of the manufacturing clause:

This version of the manufacturing clause was included in the Copyright Act of 1976. It stated that no more than 2,000 copies of a non-dramatic English-language literary work by an American author could be imported unless the material was manufactured in Canada or the United States. This clause expired in 1986.

If a publisher in Japan wanted to import 3,000 copies of a novel by an American author, they would not be allowed to do so under the manufacturing clause (1976) unless they had the books printed in Canada or the United States.

The manufacturing clause of 1909 limited copyright protection for English-language books and periodicals to those printed in the United States.

If a British publisher printed a book in English and wanted to sell it in the United States, they would not be able to claim copyright protection under the manufacturing clause (1909) unless they had the book printed in the United States.

Overall, the manufacturing clause was designed to protect American authors and publishers from foreign competition. By limiting the importation of certain works, the clause helped to ensure that American authors and publishers could profit from their creations.