The Principles of War
Philip [of Macedon], Alexander [the Great]'s father, said that it is better to have an army of deer commanded by a lion than an army of lions commanded by a deer; Alexander himself told his men that their greatest advantage was that their leader was Alexander. Alexander lived and practiced what modern (Western) military theorists teach to their pupils as the principles of war. The principles were developed out of an analysis of Napoleon's campaigns and today are supposed to guide military officers in the practice of their profession and to guide historians in their analysis of campaigns and leadership. The principles are (in order of importance): the objective, the offensive, surprise, mass and economy of force, security, unity of command, maneuver, and simplicity.
The number and order of the principles varies across countries and cultures. For a sample, see the Wikipedia entry for the Principles of War.