International copyright was slow to develop, but as global trade increased, so too did the need for an international agreement on copyright. The Berne Convention is one of those agreements. The US was one of the last developed countries to sign on. You can check out this page for more on the complex history of the US and international copyright law. There are currently 178 countries in the Berne Convention out of 195 total countries in the world (a current list updated regularly can be found here).
The Berne Convention specifies a minimum copyright term of the life of the author plus 50 years for its signatories. This doesn’t limit the signatories to just that length, though, so determining the question of whether a work is in the public domain can be complex. The US has increased that minimum to the life of the author plus 70 years, and there are countries whose copyright terms are even longer. In general, assume the typical US term of copyright protection even if the work would already be in the public domain in its home country. If the home country’s term is longer than that of the US, then we can run into a situation where the work is in the public domain in the US, but since it is not at that status in its home country, we are unlikely to find the text freely available online as we would US-published public domain works. In that situation, feel free to use the work as desired, but be wary of posting it on the open web, since that can be accessed internationally.
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