APA (7th ed.) Citation

Singer, B. (1923). Occupation of the Ruhr. [publisher not identified].

Chicago Style (17th ed.) Citation

Singer, Berhold. Occupation of the Ruhr. [Chicago?]: [publisher not identified], 1923.

MLA (9th ed.) Citation

Singer, Berhold. Occupation of the Ruhr. [publisher not identified], 1923.

Warning: These citations may not always be 100% accurate.