According to Sunzi, a state should not begin a war unless definite advantages are foreseen; indeed, aggressive war should be avoided unless the situation is absolutely critical and no alternative exists. In determining whether war should be waged, questions should be raised regarding not only its moral basis but also season and weather, the kind of terrain to be traversed, the qualities necessary to a competent commander, and army organization and discipline. Success also depends on the internal harmony (dao) of the state; without such harmony, the state’s efforts in war will fail. One should never engage in a protracted war, which is likely to result in military defeat and heavy financial deficit.
In waging war, deception is the key to success and attacks should always be conducted according to a coherent strategy. Indeed, supreme military excellence consists of breaking the enemy’s resistance without fighting. The best tactics involve blocking the enemy’s plans. The worst tactics involve besieging walled cities and fighting in mountains. The best strategy is always a balancing of the possibilities for victory. The good commander places himself in an invulnerable position and then watches for a favorable opportunity to defeat the enemy. Good tactics involve varying the concentration and division of forces. No one should attempt to wage war without knowing the topography of the territory involved. Above all, if a general fails to acquaint himself with the character of the enemy, whatever he does will lead to ruin. What enables a general to employ stratagems and deception is his knowledge of the enemy. Such information can be obtained only by means of espionage. Captured spies should be well treated and should be turned into defectors and double agents.