APA (7th ed.) Citation

De Groot, G. J. (2001). The First World War. Palgrave.

Chicago Style (17th ed.) Citation

De Groot, Gerard J. The First World War. Basingstoke [etc.]: Palgrave, 2001.

MLA (9th ed.) Citation

De Groot, Gerard J. The First World War. Palgrave, 2001.