Nit-pick: automatic copyright came about in the US via the Copyright Act of 1976, which came into force in 1978. The Berne Implementation Act of 1988 finished the job of making the US compatible [1] with Berne that the 1976 Act started.
[1] There is an argument to be made that US copyright law still isn't compatible with Berne, but the rest of the world has decided having the US in Berne is important enough that as long as US law is close enough that you can make a hand wavy argument that isn't completely ridiculous everyone lets it slide.
[1] There is an argument to be made that US copyright law still isn't compatible with Berne, but the rest of the world has decided having the US in Berne is important enough that as long as US law is close enough that you can make a hand wavy argument that isn't completely ridiculous everyone lets it slide.