Columbia subject headings:
Coal miners--Political activity--Wales--History--20th century.
Communism--Wales.
Public opinion--Wales.
Spain--History--Civil War, 1936-1939--Foreign public opinion, Welsh.
Spain--History--Civil War, 1936-1939--Participation, Welsh.
Wales--Politics and government--20th century.
Welsh--Spain--History--20th century.
Harvard subject headings:
Coal miners--Political activity--Wales--History--20th century.
Coal miners--Wales--Political activity--History--20th century.
Communism--Wales.
Public opinion--Wales.
Spain--History--Civil War, 1936-1939--Foreign public opinion, Welsh.
Spain--History--Civil War, 1936-1939--Participation, Welsh.
Wales--Politics and government--20th century
Welsh--Spain--History--20th century
Princeton subject headings:
Miners--Wales--Political activity.
Spain--History--Civil War, 1936-1939--Foreign participation--Welsh.
Spain--Relations--Wales.
Wales--Relations--Spain.