The Berne Convention for the Protection of Literary and Artistic Works is the reference international treaty on copyright. It imposes a minimum uniform level of protection for creative works in all adhering states. Significant principles include the duration of protection—equivalent to the author's lifetime plus 50 years after their death (a duration many member states have extended)—and automatic protection, which ensures the protection of works without the need for formalities or registrations.
https://www.wipo.int/wipolex/en/treaties/textdetails/12214