The place where we will fight cannot be known by the enemy. Uncertain of the battlefield, they must guard everywhere. The more places they defend, the fewer troops they can confront us with.
If they reinforce the front, their rear grows weak; if they secure the rear, their front is thin. If they strengthen the left, the right is vulnerable; if they guard the right, the left lacks strength. To defend every spot is to be weak everywhere.
Troops become weak when forced to guard against others. Troops stay strong when they make others guard against them.
Note
A great military strategist and thinker in ancient China, who lived in the late Spring and Autumn Period. He authored The Art of War, the world’s earliest and most influential military classic. His strategic thoughts have been widely applied in military, politics and management worldwide.
Sun Tzu delivers a groundbreaking logic of information and troop deployment here. Total troop numbers do not decide victory; control over the enemy’s defense layout does.
If your attack routes and target regions stay completely concealed, the enemy has no way to judge where you will strike next. To avoid being caught off guard, they have to split their limited army to cover all borders, passes and cities. Every extra defensive post drains manpower from their key strongholds. No matter how large their overall army is, scattered garrisons make them outnumbered wherever you launch your concentrated assault.
The core contrast Sun Tzu draws is clear: Passive defenders who guard against unknown threats will always be weak. Clever attackers who hide their plans force rivals into scattered defense and seize overwhelming local superiority.
This is the foundation of the tactic “I concentrate while the enemy divides”.
Unknown battlefield
Keep the enemy in the dark about your operational targets.
Dispersed defense
Defending multiple positions leads to weakness everywhere.
Active and passive defense
A key distinction – making the enemy defend you puts you in the dominant position.
Historical Case: Wu Zixu’s Three-Detachment Raid Strategy to Exhaust Chu
Chu was the dominant power in southern China with vast territory and a massive standing army. King Helü of Wu planned to conquer Chu, yet Wu’s total troops were far smaller. Wu Zixu, the state’s chief strategist, crafted a brilliant long-term harassment scheme fully aligned with Sun Tzu’s idea of concealing battle zones to split enemy forces.
It is worth pointing out that Sun Wu(Sun Tzu), the author of The Art of War, was the chief architect of this largest military campaign Wu had ever launched since its founding. King Helü of Wu appointed Sun Wu as the commanding general, with Wu Zixu and Bo Pi serving as his deputy generals, granting Sun Wu supreme battlefield command authority.
King Helü of Wu consulted Wu Zixu about strategies and tactics to defeat the State of Chu. Wu Zixu replied:
“Chu has numerous governing ministers who hold conflicting opinions, and none of them is willing to take full responsibility for military crises. If Your Majesty marches out with all three armies at once, you will only exhaust your people and waste military supplies for nothing. A better plan is to send one single division first to lure Chu’s army into battle. Since Chu’s ministers dare not shoulder blame, they will definitely dispatch massive troops to counter our advance. Once Chu mobilizes its army, Your Majesty shall withdraw our troops immediately. After Chu’s soldiers march back to rest, we launch another raid again. Dragged into constant back-and-forth long marches, Chu’s troops will be worn out and lose the will to fight. At that moment, Your Majesty can deploy various schemes to stir up deeper chaos in Chu’s military and political systems, completely shattering the morale of Chu’s people. Only then, if you assemble all three armies for a full-scale invasion, will you be able to annihilate Chu utterly.”
Wu Zixu split Wu’s elite army into three independent mobile raiding corps, which took turns launching sudden border incursions at different, unpredictable sections of Chu’s long frontier. Crucially, Wu never revealed which border area would be the next target, nor did it aim for a fixed decisive battlefield.
When the first Wu detachment attacked one Chu border, the Chu court panicked. Unaware whether this raid was the main offensive or a mere feint, Chu had to mobilize its full army and march hundreds of miles to reinforce that threatened region. By the time Chu’s weary army arrived, Wu’s troops had already retreated safely back home to rest. No sooner had Chu’s soldiers dismissed to recuperate than the second Wu corps struck a totally separate stretch of Chu’s border on the opposite side.
Over years of repeated cycles, Chu was trapped in endless passive defense. Following Sun Tzu’s description: Chu “guarded the front, so its rear grew thin; guarded the west, so its east lacked troops.” Since Wu’s battle zones were always unforeseeable, Chu had to garrison every border city and mountain pass simultaneously – it defended everywhere, and thus was weak everywhere.
Chu’s army was forced to shuttle back and forth across its vast territory without sustained rest. Its soldiers, supplies and national strength were steadily drained just to guard against Wu’s unpredictable strikes. As Zuo’s Commentary records:
“From this time onward, Chu began to suffer ruinous strain.”
In line with Sun Tzu’s summary: Chu’s troops became sparse because they were forced to constantly defend against Wu’s unknown attacks. Wu’s small detachments gained relative numerical advantage in every single skirmish, because Wu made Chu split its huge army to cover all potential battlefields. This prolonged exhaustion strategy laid the groundwork for Wu’s decisive triumph in the Battle of Bo Ju years later, when Wu’s concentrated full army broke the already fragmented, fatigued Chu defenses.
吾所與戰之地不可知，不可知，則敵所備者多，敵所備者多，則我所與戰者寡矣。故備前則後寡，備後則前寡，備左則右寡，備右則左寡，無所不備，則無所不寡。寡者，備人者也；眾者，使人備己者也。
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