Columbia subject headings:
Latvia--History--1918-1940--Congresses.
Latvia--History--1940-1991--Congresses.
Latvia--History--1991---Congresses.
Harvard subject headings:
Latvia--Politics and government--20th century.
Princeton subject headings:
Latvia--History--1918-1940--Congresses.
Latvia--History--1940-1991--Congresses.
Latvia--History--1991---Congresses.