APA (7th ed.) Citation

Library of Congress. Research Services. (1921). Classification: Universal and old world history, European War, D 501-659. GPO.

Chicago Style (17th ed.) Citation

Library of Congress. Research Services. Classification: Universal and Old World History, European War, D 501-659. [Washington]: GPO, 1921.

MLA (9th ed.) Citation

Library of Congress. Research Services. Classification: Universal and Old World History, European War, D 501-659. GPO, 1921.