However, the United States did not join the Berne Convention until 1988, and prior to 1978 it did not automatically grant federal copyright when a work was crea

However, the United States did not join the Berne Convention until 1988, and prior to 1978 it did not automatically grant federal copyright when a work was created; instead you had to register your work with the Copyright Office in order to receive federal protection. There were also some state-level protections at the time that did not require registration, but apparently they weren't very strong.