Sun Tzu was a Chinese military general, strategist, philosopher, and writer who lived during the Eastern Zhou period (771–256 BC). Sun Tzu is traditionally credited as the author of The Art of War, an influential work of military strategy that has affected both Western and East Asian philosophy and military thought. Sun Tzu mastered the military science of ancient China and created the military doctrine of asymmetrical warfare. According to it, an attack on the enemy should begin only after the enemy has no opportunity to either defend or counterattack.