These are the words of Master Sun:
To field a thousand light chariots and a thousand heavy chariots as support for a hundred thousand mail-clad soldiers with enough supplies to march three hundred miles costs a great fortune. And that is not the only expense a sovereign must endure as he wages war. He must also pay for the entertainment of important guests to the state, for the repair of chariots and chain-mail armor, and even for little things such as lacquer and glue for shields and armor.
A prolonged war will weaken the discipline and morale of your troops and dull their weapons. If you lay siege to a city, you will slowly but surely use up your strength. If your campaign grows prolonged, it will drain the resources of the state until the state can no longer bear the burden of war. And when your strength has been sapped, other sovereigns will notice and take advantage of your weakness. No man, no matter how wise, can avoid this.
Thus, though it is foolish to be hasty in the waging of war, there is no wisdom in prolonging it either. I can think of no instance in which a state has gained any advantage from prolonging a war.
Only a commander who fully knows the evils of war will truly know how to lead an army into war.
The skillful commander will only conscript the citizenry once. He will also only load his supply wagons once. He will bring the materials for war from home, but he will loot the enemy for supplies. In this way he will make sure his army is well provisioned.
The coffers of the state are quickly emptied if you supply your army from your home provinces. The people will grow poor if you supply your army with food over great distances, and prices will rise when your army is near, which in turn will also impoverish the people. And that is not all, for when the state's coffers have been emptied the people will have to suffer the levying of war taxes. Soon the people will have lost all the necessities of life, and the common man will have seen his estate used up and destroyed. The state at the same time will be using a greater and greater percentage of its revenue to replace draught oxen and heavy wagons, broken chariots and worn-out horses, new chain-mail armor and helmets, new bows, arrows, spears, shields, and the many other requirements of war.
A clever commander therefore loots his enemy. A single wagon of enemy supplies is worth twenty of your own, and a single bucketful of fodder from the enemy is worth twenty from your own stockpiles.
To beat your enemy, you need to rouse the anger of your troops, and they need to be able to see an advantage for themselves in achieving victory. You should therefore reward your troops with riches and glory. Reward those who capture the first chariot from the enemy. Replace the banner on this stolen chariot with your own banner and field it among your own chariots. Treat prisoners kindly. You may in this way augment your strength on the back of a conquered enemy.
Make sure that victory is always your objective, and avoid a lengthy campaign.
Understanding all this reveals the fact that a commander well versed in the art of war serves the interest of the people, as the commander alone determines whether the state survives or perishes.