In this atmosphere, military advisors became as important as the civil bureaucrats, and military strategy began to inform political thinking. The most influential work on the subject was The Art of War, believed to have been written by Sun Tzu, a general in the army of the king of Wu. The opening passage reads: “The art of war is of vital importance to the state. It is a matter of life and death, a road either to safety or to ruin. Hence it is a subject of inquiry which can on no account be neglected.” This marked a distinct break from the political philosophy of the time, and Sun Tzu’s work was perhaps the first explicit statement that war and military intelligence are critical elements of the business of the state. The Art of War deals with the practicalities of protecting and maintaining the prosperity of the state. Where previous thinkers had concentrated on the structure of civil society, this treatise focuses on international politics, discussing public administration only in connection with the business of planning and waging wars, or the economics of maintaining military and intelligence services.

  Sun Tzu’s detailed description of the art of war has been seen as providing a framework for political organization of any sort. He gives a list of the “principles of war” that are to be considered when planning a campaign. In addition to practical matters, such as weather and terrain, the list includes the moral influence of the ruler, the ability and qualities of the general, and the organization and discipline of the men. Implicit in these principles of war is a hierarchical structure with a sovereign at its head, taking advice from and giving commands to his generals, who lead and organize their troops.

  For Sun Tzu, the role of the sovereign is to provide moral leadership. The people must be convinced that their cause is just before they will give their support, and a ruler should lead by example; this was an idea that Sun Tzu shared with Confucius. Like the bureaucrat of civil society, the general acts as both advisor to the ruler and administrator of his commands.

  Unsurprisingly, Sun Tzu places great emphasis on the qualities of the general, describing him as the “bulwark of the state.” His training and experience inform the counsel he gives the sovereign, effectively determining policy, but are also vital to the organization of the army. At the head of the chain of command, he controls the logistics, and especially the training and discipline of the men. The Art of War recommends that discipline be rigorously enforced with harsh penalties for disobedience, but that this should be tempered by a consistent application of rewards and punishments.

A terra-cotta army was built to line the tomb of Emperor Qin Shi Huang, showing the importance of the military to him. Qin lived 200 years after Sun Tzu, but would have read his works closely.

While this description of a military hierarchy mirrored the structure of Chinese society, The Art of War was much more innovative in its recommendations for international politics. Like many generals before and since, Sun Tzu believed that the purpose of the military was to protect the state and ensure its welfare, and that war should always be a last resort. A good general should know when to fight and when not to fight, remembering that an enemy’s resistance can often be broken without armed conflict. A general should first try to thwart the enemy’s plans; failing that, he should defend against attack; only failing that should he launch an offensive.

To avoid the necessity for war, Sun Tzu advocated maintaining a strong defense and forming alliances with neighboring states. Since a war is harmful to both sides, it often makes sense to come to a peaceful settlement. Prolonged campaigns, especially tactics such as laying siege to an enemy’s city, are such a drain on resources that their cost often outweighs the benefits of victory. The sacrifices that have to be made by the people put a strain on their loyalty to the moral justness of the cause.

The key to stable international relationships, argues Sun Tzu, is intelligence, which was then the responsibility of the military. Spies provide vital information on a potential enemy’s intentions and capabilities, allowing the generals who command the spies to advise the ruler on the likelihood of victory in the event of conflict. Along the same lines, Sun Tzu goes on to explain that the next most important element in this information warfare is deception. By feeding misinformation to the enemy about defenses, for example, war can often be averted. He also advised against what he saw as the folly of attempting to destroy an enemy in battle: this decreased the rewards that could be gained from the victory—both the goodwill of any defeated soldiers and the wealth of any territory gained.

Underlying the very practical advice in The Art of War is a traditional cultural foundation based on moral values of justice, appropriateness, and moderation. It states that military tactics, international politics, and war exist to uphold these values and should be conducted in accordance with them. The state exercises its military capability to punish those that harm or threaten it from outside, just as it uses the law to punish criminals within it. When done in a morally justifiable way, the state is rewarded by happier people and the acquisition of territory and wealth. The Art of War became an influential text among the rulers, generals, and ministers of the various states in the struggle for a unified Chinese empire. It was later an important influence on the tactics of revolutionaries, including Mao Zedong and Ho Chi Minh. It is now required reading at many military academies, and is often included as a set text in courses on politics, business, and economics.

The Great Wall of China, begun in the 7th century BCE, acted to fence off newly conquered territories. For Sun Tzu, such defensive measures were as important as attacking force.