No, the US could not do that and there is multiple reasons for it. The root zone is rather special in that operating system semi-hard code the root servers. The operating system also have full control here and the number of name servers at the root zone changes very slowly. Operating systems developed by people not bound by US courts could just ignore it.

The other reason is political. If they were to cut out eu or asia from the list then the risk of a split would increase massively. It would be suicide. If they did that people might even split internet further by splitting iana (Internet Assigned Numbers Authority), in which case a computer in EU would be unable to communicate with an computer in US, and then the concept of a global internet would no longer exist. A split is a exceedingly dangerous concept.