Columbia subject headings:
Harvard subject headings:
Lower Saxony (Germany)--Foreign relations--Russia.
Lower Saxony (Germany)--History--Sources.
Niedersächsisches Landesarchiv.
Royal houses--Germany--Lower Saxony--History.
Royal houses--Russia--History.
Russia--Foreign relations--Germany--Lower Saxony.
Russia--History--Sources.
Princeton subject headings:
Oldenburg family.
Russia.