SUN ZI said: In respect of the employment of troops, ground may be classified as dispersive, frontier, key, open, focal, serious, difficult, encircled, and desperate.  When a chieftain is fighting in his own territory, he is in dispersive ground. When he has penetrated into hostile territory, but to no great distance, he is in frontier ground.  Ground equally  advantageous  for us and the enemy to occupy is key ground.  Ground equally accessible to both sides is open.  Grouna contiguous to three other  states is focal.  He who first gets control of it will gain the support of the majority of neighbouring  states.  When an army has  penetrated deep  into hostile territory, leaving far behind many enemy cities and towns, it is in serious ground.  Mountain forests, rugged steeps, marshes, fens and all that is hard to traverse fall into the category of difficult ground.  Ground to which access is constricted and from which we can only retire by tortuous paths so that a small number of the enemy would suffice to crush a large body of our men is encircled ground.  Ground on which the army can avoid annihilation only through a desperate fight without delay is called a desperate one.  And,  therefore, do not fight in dispersive  ground; do not stop in the frontier borderlands.  Do not attack an enemy who has occupied key ground; in open ground, do not allow your communication to be blocked.  In focal ground,  form alliances with neighbouring states; in serious ground, gather in plunder.  In difficult ground, press on; in encircled ground, resort to stratagems; and in desperate ground, fight courageously.

    In ancient times, those described as skilled in war knew how to make it impossible for the enemy to unite his van and his rear, for his large and small divisions to cooperate, for his officers and men to support each other, and for the higher and lower levels of the enemy to establish contact with each other.  When the enemy's forces were dispersed, they prevented him from assembling them; even when assembled, they managed to throw his forces into disorder. They moved forward when it was advantageous to do so; when not advantageous, they halted.  Should one ask:  'How do I cope with a well-ordered enemy host about to attack me?' I reply: 'seize something he cherishes and he will conform to your desires.' Speed is the essence of war.  Take advantage of the enemy's unpreparedness,  make your way by unexpected routes, and attack him where he has taken no precautions.

    The general principles applicable to an invading force are that the deeepr you penetrate into hostile territory, the greater will be the solidarity of your troops, and thus the defenders cannot overcome you.  Plunder fertile country to supply your army with plentiful food.  Pay attention to the soldiers' well-being and not fatigue them.  Try to keep them in high  spirits and conserve their energy.  Keep the army moving and devise  unfathomable plans.  Throw your soldiers  into a positon whence there is no escape, and they will choose death over desertion. For if prepared to die, how can the officers and men not exert  their uttermost strength to fight?  In a desperate situation, they fear nothing; when there is no way out, they stand firm.  Deep in a hostile land they are bound together.  If there is no help for it, they will fight hard. Thus, without waiting to be marshalled, the soldiers will be constantly vigilant;  without waiting to be asked, they will do your will; without restrictions, they will be faithful; without giving orders, they can be trusted.  Prohibit superstitious practices and do away with rumours, then nobody will flee even facing death. Our soldiers have no surplus of wealth,  but it is not because they disdain riches; they have no expectation of long life, but it is not because they dislike longevity.  On the day the army is ordered  out to battle, your soldiers may weep,  those sitting up wetting their garments, and those lying down letting the tears run down their cheeks.  But throw them into a situation where there is no escape and they will display the immortal courage of Zhuan Zhu and Cao Kuei.

    Troops directed by a skilful general are comparable to the Shuai Ran.  The Shuai Ran is a snake found in Mount Heng.  Strike at its head, and you will be attacked by its tail; strike at its tail, and you will be attacked by its head; strike at its middle, and you will be attacked by both its head and its tail.  Should'one ask:  'Can troops be made capable of such instantaneous coordination as the Shuai Ran?' I reply:  'They can.'  For the men of Wu and the men of Yue are enemies, yet if they are crossing a river in the same boat and are caught by a storm, they will come to each other's assistance just as the left hand helps the right.  Hence, it is not sufficient to rely upon tethering of the horses and the burying of the chariots.  The principle of military administration is to achieve a uniform level of courage.  The principle of terrain  application is to make the best use of both the high and the low-lying grounds. Thus, a skilful general conducts his army just as if he were leadinto a perilous situation and they will survive; put them in desperate ground and they will live.  For when the army is placed in such a situation, it can snatch victory from defeat.  Now, the key to military operations lies in cautiously studying enemy's designs. Concentrate your forces in the main direction against the enemy and from a distance of a thousand Ii you can kill his general.  This is called the ability to achieve one's aim in an artful and ingenious manner.

    Therefore, on the day the decision is made to launch war, you should close the passes, destroy the official tallies, and stop the passage of all emissaries.  Examine the plan closely in the temple council and make final arrangements.  If the enemy leaves a door open, you must rush in.  Seize the place the enemy values without making an appointment for battle with him.  Be flexible and decide your line of action according to the situation on enemy side.  At first, then, exhibit of coyness of a maiden until the enemy gives you an opening;  afterwards be swift as a running hare, and it will be too late for the enemy to oppose you.