APA (7th ed.) Citation

Thornton, A. P. (1978). Imperialism in the twentieth century / by A.P. Thornton. Macmillan.

Chicago Style (17th ed.) Citation

Thornton, A. P. Imperialism in the Twentieth Century / by A.P. Thornton. London (etc.): Macmillan, 1978.

MLA (9th ed.) Citation

Thornton, A. P. Imperialism in the Twentieth Century / by A.P. Thornton. Macmillan, 1978.

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