War is a life-and-death matter of the utmost importance to the State. Five factors decide the outcome of war: the “Moral Law,” or good governance; “Heaven,” or weather and season; “Earth,” or geography; “The Commander,” or the quality of the military leader; and “Method and Discipline,” or the quality of the army (1.4). Whichever side makes better use of these five factors will win.

Warfare relies on deception. Armies should seem strong when they are weak and unprepared when they are ready to fight. If evenly matched, opponents must remain prepared; when overmatched, they must avoid conflict. An irritable opponent should be goaded; attacks should be launched when and where they are least expected. The general who plans carefully will overpower the one who makes hasty calculations.

Taking all expenses, large and small, into account, raising an army of 100,000 men costs 1,000 ounces of silver per day. A protracted siege can dry up a country’s resources, and other states may suddenly attack.

Wise generals will bring weaponry from home but feed their armies on the bounty of the country they invade. Weapons captured during battle can be turned against the enemy.