The story that made Sun Tzu a person was written some four hundred years after he is supposed to have lived. Around 100 BCE Sima Qian, the Han court historian, recorded that a man named Sun Wu, from the state of Qi, brought thirteen chapters on war to King Helü of Wu, a kingdom on China's south-eastern coast. The king asked for a demonstration using the women of his palace. Sun Wu drilled them in two companies, each led by one of the king's favourite concubines, and when the women laughed at his orders he had the two leaders executed, over the king's protest. After that the orders were obeyed. Helü made him a general, and Sima Qian gives him a share in Wu's victory over the powerful state of Chu in 506 BCE.
The record of his own age is silent. The Zuo zhuan, the chronicle that tells Wu's war with Chu in detail, has no Sun Wu in it, as the Song-dynasty scholar Ye Shi pointed out around 1200. Modern historians add that generals who were professionals, rather than noblemen commanding by right of birth, appear only in the Warring States period that followed, from the fifth century BCE, and many date the book to that age. The dates usually printed for him, about 544 to 496 BCE, are traditional. Whether he lived at all is disputed, and the book may be the work of more than one hand.
What the book answers is clearer than who wrote it. It speaks to rulers whose states fielded armies of a hundred thousand men — the book's own figure — and could be erased by one lost war. Its opening premise is that war decides whether a state lives or dies, and must be studied for that reason and no other. From there it counts costs. A long campaign empties the treasury and invites the neighbours in; a siege spends months building engines and then throws away a third of the attackers; no country, it says, has ever gained from a prolonged war. Victory depends first on knowledge, and knowledge of the enemy comes from people, never from spirits or omens. Before any fighting, the general compares the two sides on a short list of factors: the ruler's conduct, weather and season, terrain, the commander, discipline. He feigns weakness when he is strong and distance when he is near, and pays his spies better than anyone else in the army.
The claim Sun Tzu is remembered for follows from that arithmetic: the highest skill in war is to subdue the enemy without a battle, by defeating his plans and breaking his alliances before an army ever takes the field. It sounds gentler than it is. The reasoning is about cost, and the same thirteen chapters recommend baiting the enemy with small gains, buying his spies over to the general's own side and setting his camp on fire.
The book's later history is far better recorded than its author. In 1972 archaeologists at Yinqueshan, in Shandong, opened a Han tomb sealed in the late second century BCE and found bamboo slips carrying a text close to the one read today, and beside it the lost Military Methods of Sun Bin, a fourth-century BCE strategist whom Sima Qian calls Sun Wu's descendant. The warlord Cao Cao wrote the oldest surviving commentary around 200 CE, and in 1080 the Song court set the book among its Seven Military Classics. Takeda Shingen, a sixteenth-century Japanese warlord, took the words on his battle standard from it. In December 1936, in an essay on the strategy of China's revolutionary war, Mao Zedong cited its rule that a commander who knows the enemy and knows himself need not fear defeat.