Columbia subject headings:
Harvard subject headings:
Europe--Politics and government--Congresses.
Marriages of royalty and nobility--Europe--History--Congresses.
Queens--Europe--Biography--Congresses.
Princeton subject headings:
Europe--Politics and government--History--Congresses.
Europe--Relations--Congresses.
Nobility--Political activity--Europe--History--Congresses.
Politics and culture--Europe--History--Congresses.
Power (Social sciences)--Europe--History--Congresses.
Queens--Europe--History--Congresses.
Queens--Political activity--Europe--History--Congresses.