Schmitt, Carl. The Concept of the Political. Trans. George Schwab. Chicago: Univ. of Chicago Press, 1996.
Originally published in German in 1932 as Der Begriff des Politischen, this work provided Yockey with his philosophy of politics. Schmitt argues that the disjunction friend/enemy is as vital to politics as the disjunction good/bad, beautiful/ugly, true/false are to (respectively) ethics, aesthetics, and logic.
Spengler, Oswald. The Decline of the West. 2 vols. trans. by Charles Francis Atkinson. New York: Alfred A. Knopf, 1950.
Originally published in German in 1918 as Der Untergang des Abendlandes, this work is a philosophy of history as prose threnody. Yockey's work is a sequel to and application of Spengler's. A basic understanding of Spengler's method and vocabulary is essential to reading Yockey.
Yockey, Francis Parker. Imperium: The Philosophy of History and Politics. Sausalito, Calif.: Noontide Press, 1962.Yockey's work is still in print in paperback format and may be order from most booksellers.