Coba jelasin Sumber sekunder dari Terorisme dan Komunisme dong

Baruch Knei-Paz, The Social and Political Thought of Leon Trotsky. Oxford, England: Oxford University Press, 1978.

Massimo L. Salvadori, Karl Kautsky and the Socialist Revolution, 1880-1938. Jon Rothschild, trans. London: New Left Books, 1979.

Gary P. Steenson, Karl Kautsky, 1854-1938: Marxism in the Classical Years. Pittsburgh, PA: University of Pittsburgh Press, 1978.