Columbia subject headings:
Black Sea Region--Environmental conditions.
Black Sea Region--Politics and government.
Black Sea Region--Relations--European Union countries.
Harvard subject headings:
Black Sea Region--Politics and government--20th century.
Black Sea Region--Politics and government--21st century.
Geopolitics--Black Sea Region.
National security--Black Sea Region.
Princeton subject headings:
Black Sea Region--Politics and government--20th century.
Black Sea Region--Politics and government--21st century.
Geopolitics--Black Sea Region.
National security--Black Sea Region.