The Principles of War

As defined in the U.S.Army Field Manual FM-3 Military Operations.

Principle Definition
Objective Direct every military operation towards a clearly defined, decisive, and attainable objective.
Unity of command For every objective, ensure unity of effort under one responsible commander.
Offensive Seize, retain, and exploit the initiative.
Mass Concentrate combat power at the decisive place and time.
Economy of force Allocate minimum essential combat power to secondary efforts.
Maneuver Place the enemy in a position of disadvantage through the flexible application of combat power.
Surprise Strike the enemy at a time, at a place, or in a manner for which he is unprepared.
Security Never permit the enemy to acquire an unexpected advantage.
Simplicity Prepare clear, uncomplicated plans and clear, concise orders to ensure thorough understanding.

An additional principle, taught in some armies

AnnihilationNever fight the same enemy twice.