Columbia subject headings:
Bulgaria--Foreign relations--Great Britain.
Great Britain--Foreign relations--Bulgaria.
World War, 1939-1945--Bulgaria.
World War, 1939-1945--Great Britain.
Harvard subject headings:
Bulgaria--Foreign relations--Great Britain.
Great Britain--Foreign relations--Bulgaria.
World War, 1939-1945--Bulgaria.
World War, 1939-1945--Great Britain.
Princeton subject headings: