APA (7th ed.) Citation

Keegan, J. (1999). The First World War (1. American ed.). Knopf.

Chicago Style (17th ed.) Citation

Keegan, John. The First World War. 1. American ed. New York: Knopf, 1999.

MLA (9th ed.) Citation

Keegan, John. The First World War. 1. American ed. Knopf, 1999.