Columbia subject headings:
Borderlands--History.
Boundaries--Political aspects--History.
Colonization--History.
Emigration and immigration--History.
Globalization--History.
Imperialism--History.
Walls--Political aspects--History.
World history.
Harvard subject headings:
Borderlands--History.
Boundaries--Political aspects--History.
Colonization--History.
Emigration and immigration--History
Globalization--History
Imperialism--History
Walls--Political aspects--History.
World history
Princeton subject headings:
Borderlands--History.
Boundaries--Political aspects--History.
Colonization--History.
Emigration and immigration--History.
Globalization--History.
Imperialism--History.
Walls--Political aspects--History.
World history.