APA (7th ed.) Citation

Black, C. E., & Helmreich, E. C. (1972). Twentieth century Europe: A history (4. ed.). Knopf.

Chicago Style (17th ed.) Citation

Black, Cyril Edwin, and Ernst Christian Helmreich. Twentieth Century Europe: A History. 4. ed. New York: Knopf, 1972.

MLA (9th ed.) Citation

Black, Cyril Edwin, and Ernst Christian Helmreich. Twentieth Century Europe: A History. 4. ed. Knopf, 1972.