MacLean, Paul D. The Triune Brain in Evolution: Role in Paleocerebral Functions. New York and London: Plenum Press, 1990. Paul D. MacLean contends that the human brain is made up of three separate brains, which function together interactively in the way that he characterizes as constituting the triune human brain. What MacLean refers to as the reptilian brain is the biological base for all agonistic tendencies in all animals, including the human animal.
Maier, Pauline; Merritt Roe Smith; Alexander Keyssar; and Daniel J. Kevles. Inventing America: A History of the United States, 2nd ed. New York and London: W. W. Norton, 2006. Very accessible and thorough textbook about the agonistic spirit as inventive. Also published in a two-volume paperback edition.
Moore, Robert and Douglas Gillette. The Warrior Within: Accessing the Knight [Archetype] in the Male Psyche. New York: William Morrow, 1992. Very accessible. (There is a corresponding Warrior archetype in the female psyche.)
Nagy, Gregory. The Best of the Achaeans: Concepts of the Hero in Archaic Greek Poetry, 2nd ed. Baltimore, Maryland; and London, England: JohnsHopkinsUniversity Press, 1998.