Comment by Archelaos

The incompatiblity of U.S. and German copyright law is not so much in the momentary duration, which in both jursidictions is 70 years after the author's death (exceptions apply to anonymous publications). The major incompatiblities arise from the regulations which were in place before the durations were harmonized (for the U.S., prior to 1978).

On an international scale, the situation is more complicated. Rougly speaking, the range for the duration of copyright is from "life + 50 yrs" up to "life + 100 yrs". Wikipedia has a list of these.[1] There are many countries where works from up to the early 1970s are already in the public domain that are still under copyright protection in the U.S. for up to the next 20 years. In principle, problems may arise if the country in which a work is published in the Internet sets a shorter term of protection than the maximum term in this list.

[1] https://en.wikipedia.org/wiki/List_of_countries%27_copyright...