What "Jusidiction" does congress have to grant such jurisdiction to our Federal Courts? None. The Constitution doesn't grant them power over Croatia and its past crimes or actions. As far as I know, there is no binding treaty on Croatia that cedes this power to the United States either. Without Jurisdiction, it makes any hearing a Kangaroo Court. . . with no power to enforce any decision it may come to.
Section 2.
between Citizens of different States,—between Citizens of the same State claiming Lands under Grants of different States, and between a State, or the Citizens thereof, and foreign States, Citizens or Subjects.