APA (7th ed.) Citation

Pius XI, P. (1967). Essays in history: Written between the years 1896-1912. Books for Libraries Press.

Chicago Style (17th ed.) Citation

Pius XI, Pope. Essays in History: Written Between the Years 1896-1912. Freeport, N.Y.: Books for Libraries Press, 1967.

MLA (9th ed.) Citation

Pius XI, Pope. Essays in History: Written Between the Years 1896-1912. Books for Libraries Press, 1967.