Columbia subject headings:
Communism--History.
Communism--Soviet Union--History--20th century.
Fourth International--History.
Trotsky, Leon, 1879-1940.
Harvard subject headings:
Communism--History--20th century
Communism--Soviet Union--History
Fourth International--History.
Trotsky, Leon, 1879-1940
Princeton subject headings:
Communism--History--20th century.
Communism--Soviet Union--History--20th century.
Fourth International--History.
Trotsky, Leon, 1879-1940.