Columbia subject headings:
Harvard subject headings:
Balkan Peninsula--Boundaries--History--21st century.
Balkan Peninsula--Emigration and immigration--History--21st century.
Balkan Peninsula--Politics and government--1989-
Border crossing--Balkan Peninsula--History--21st century.
Border security--Balkan Peninsula--History--21st century.
National security--Balkan Peninsula--History--21st century.
Princeton subject headings:
Balkan Peninsula--Boundaries--History--21st century.
Balkan Peninsula--Emigration and immigration--History--21st century.
Balkan Peninsula--Politics and government--1989-
Border crossing--Balkan Peninsula--History--21st century.
Border security--Balkan Peninsula--History--21st century.
National security--Balkan Peninsula--History--21st century.