APA (7th ed.) Citation

Oman Sir. (1998). A history of the art of war in the Middle Ages. Greenhill Books.

Chicago Style (17th ed.) Citation

Oman Sir. A History of the Art of War in the Middle Ages. London: Greenhill Books, 1998.

MLA (9th ed.) Citation

Oman Sir. A History of the Art of War in the Middle Ages. Greenhill Books, 1998.

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