APA (7th ed.) Citation

Christopher, A. J. (1988). The British empire at its Zenith. Croom Helm.

Chicago Style (17th ed.) Citation

Christopher, Anthony J. The British Empire at Its Zenith. London: Croom Helm, 1988.

MLA (9th ed.) Citation

Christopher, Anthony J. The British Empire at Its Zenith. Croom Helm, 1988.