alt Hacker NewsTake an extreme hypothetical. Suppose in the 1500s the government of Spain had taken some artifacts relating to the indigenous peoples of New Mexico. Would the government of the United States really be the rightful owner of these artifacts?
For other countries it's not quite as extreme, but in general the link between ancient culture in place X and modern country in place X is less strong than people try to make out.
I don’t see the controversy of your example because since there was no UNESCO and other global agreements in the 1500s, the indigenous people of this area are still around and so it would be the local Native American tribes that can have a legitimate claim on their heritage.