I am not a copyright law expert. But the Berne Convention originally dates to 1886.

There is apparently some flexibility within the Berne Convention on copyright terms. There are also limitations on public domain works in continental Europe that differ from common law countries like the US. However, it does govern copyright in broad strokes. For example, the US used to require that a creator explicitly assert copyright while most of the rest of the world did not.

In any case, the US is generally aligned with copyright in most of the rest of the world. So any broad change in copyright law (other than perhaps somewhat shortening terms) would make it an outlier.