The Cost of War: A Tongjian Lesson

War in the Zizhi Tongjian is never just a military event. Sima Guang documents every major campaign with attention to its fiscal, social, and institutional costs. The Tongjian does not pacifist. It records successful wars that expanded territory, secured frontiers, and protected populations. But it also records, with equal diligence, the cost of those wars to the societies that paid for them. The lesson Sima Guang consistently draws is that war is a test of institutional capacity as much as military capability, and the state that wins the war but loses its institutional integrity has really lost both. For more lessons for rulers, see Zizhi Tongjian’s Lessons for Rulers and Managers.

The Three Costs of War in the Tongjian

The Tongjian identifies three categories of war cost that every ruler must weigh before committing to military action. The first is fiscal: war requires money, and the money must come from taxation, borrowing, or currency debasement, each of which has consequences. The second is social: war requires soldiers, and the soldiers must come from the productive population, reducing agricultural and economic output. The third is institutional: war concentrates power in military commanders, and concentrated military power can become a threat to the state that created it.

Emperor Wu of Han: Successful Wars, Costly Victory

The Tongjian‘s treatment of Emperor Wu’s campaigns against the Xiongnu is nuanced. The campaigns were militarily successful. The Xiongnu were defeated, Han territory expanded to its greatest extent, and the frontier was secured for decades. But the costs were enormous. The treasury that Emperor Wen and Emperor Jing had carefully built up was depleted. Tax rates were raised. New taxes were created. The economic strain was compounded by Emperor Wu’s massive public works, expansion of the imperial court, and personal extravagance in his later years. The Tongjian records the fiscal details with care, noting the moment when the treasury could no longer sustain the campaigns and the state began searching for new revenue sources.

What Sima Guang shows is that even a successful war can damage the state that wages it. The Han’s military triumph under Emperor Wu came at the cost of fiscal depletion, social strain, and the concentration of military power in the hands of generals who became political figures. The institutional costs took a generation to manifest but ultimately contributed to the Wang Mang usurpation. What makes Emperor Wu’s case so valuable for students of the Tongjian is that the military success was real and the institutional damage was gradual. It took decades for the fiscal weakness, social strain, and accumulated military power to undermine the Han, and during that time the dynasty continued to function on the surface. The lesson is that war damage is not always immediate; it can work through the system slowly, like a slow-acting poison that does not kill quickly but makes the body susceptible to the next disease.

For the Tongjian, military success without institutional follow-through is incomplete. For more on the Han’s trajectory, see The Tongjian on the Founding of the Han.

The Sui Catastrophe: When All Three Costs Converge

Emperor Yang of Sui provides the Tongjian‘s clearest warning about the cost of war. His Goguryeo campaigns combined all three costs simultaneously and catastrophically. The fiscal cost: the campaigns consumed resources the Sui could not produce, requiring extraordinary taxation and forced labor. The social cost: millions of peasants were conscripted, farms were abandoned, and famine spread. The institutional cost: the military command structure was disrupted by repeated failures, leaving no clear chain of authority when revolts began.

The Tongjian presents the Sui disaster as a case study in what happens when a ruler ignores all three costs simultaneously. Each cost individually might have been manageable. Together, they created a feedback loop: fiscal strain drove higher taxation, which drove social unrest, which required military suppression, which required more fiscal resources, which drove even higher taxation. The cycle was mutually reinforcing and ultimately destroyed the dynasty. For the Sui’s story, see The Tongjian on the Sui Reunification and Collapse.

The Tongjian‘s argument about war is not that war is always wrong. It is that war is always expensive, and the expense extends far beyond the battlefield. A ruler who calculates only the military cost of war has not understood war. The true cost includes the fiscal damage, the social disruption, and the institutional distortion that can outlast the war by generations. The ruler who starts a war inherits three bills, and he must be prepared to pay all three.

War and the Degradation of Governance

The most subtle cost of war in the Tongjian is the degradation of governance that accompanies long conflicts. During a war, the military chain of command takes precedence over civilian administration. Resources are diverted from civilian programs to military ones. The normal feedback mechanisms (censorate reports, ministerial criticism, public petition) are suppressed in the name of national unity and military necessity. The Tongjian records how the Tang’s culture of open criticism, carefully maintained under Taizong, eroded during the Goguryeo and Tibetan campaigns as wartime imperatives silenced dissent.

The degradation is gradual and reversible in principle, but the Tongjian shows that reversals are rare. Once the habits of war governance become embedded, they persist into peacetime. The wartime commander who grows accustomed to overriding civilian authority does not easily surrender that authority when the war ends. The wartime taxes that were described as temporary become entrenched as the new baseline. The wartime censorship of dissent, justified by national security, becomes the new standard for acceptable court communication. The Tongjian tracks this pattern across multiple dynasties, and in each case the wartime measures outlasted the wars that created them by decades.

The most dramatic example is the Tongjian‘s treatment of the Tang jiedushi. These military governors were originally appointed as temporary commanders for specific campaigns. The pressures of the An Lushan Rebellion turned them into permanent regional authorities with combined military and civil power. When the rebellion ended, the institution did not revert to its pre-war form. The jiedushi remained, and the Tang court could not dismantle them. One wartime accommodation became a structural liability that lasted 144 years. The jiedushi system, created as a wartime measure to give commanders enough autonomy to respond quickly to threats, became a peacetime institution that no succeeding emperor could dismantle. For the Tang’s long decline, see The Tongjian on the Tang Dynasty Glory and Decline, and for the institutional dimension, see Institutional Resilience: A Tongjian Lesson.

One pattern the Tongjian documents with particular clarity is the lag between military expenditure and fiscal collapse. The costs of war do not arrive all at once. They accumulate over years, sometimes decades, as the state borrows against future revenues, defers maintenance on civilian infrastructure, and redirects administrative talent from governance to logistics. By the time the fiscal strain becomes visible, the underlying damage is already structural. Emperor Wu of Han’s campaigns against the Xiongnu, impressive in the short term, left a fiscal legacy that the Western Han never fully recovered from. The state monopolies on salt and iron, originally wartime measures, became permanent fiscal crutches that distorted the economy for the remainder of the dynasty. The Tongjian traces this slow fiscal erosion across multiple reigns, showing how the cost of one war mushrooms into the cost of a permanently altered economic structure. For the fiscal dimension of institutional decay, see Institutional Resilience: A Tongjian Lesson and the broader set of lessons.

The geopolitical dimension of war costs is another thread Sima Guang weaves through the chronicle. Wars do not happen in isolation. Each military campaign sends ripples through the diplomatic landscape, creating new allies and new enemies. The Han campaigns against the Xiongnu disrupted the steppe power balance so thoroughly that new confederations arose in the vacuum. The Tang campaigns in Central Asia created enemies among states that had previously been neutral or friendly. The Tongjian documents how the diplomatic cost of war compounds the fiscal and institutional costs, creating strategic environments that are more dangerous than the ones the war was meant to resolve.

The Tongjian‘s most valuable contribution to thinking about war costs is its longitudinal perspective. Individual campaigns are judged not by their immediate results but by the institutional and fiscal landscape they leave behind. A campaign that conquers territory but depletes the treasury is counted as a net loss. A campaign that achieves limited objectives while preserving institutional capacity is counted as a success. This framework, applied across 1,300 years of history, provides a standard of evaluation that no single ruler could construct from their own experience alone. It is the gift of Sima Guang’s comprehensive view. It shows what no participant in any single war could see: the pattern across all wars.

FAQ

Does the Tongjian ever show a war that was worth its cost?

Emperor Taizong’s campaign against the Eastern Turks is the closest the Tongjian comes to an unqualified endorsement. The campaign was quick, decisive, and followed by institutional consolidation that prevented recurrence. But Sima Guang’s endorsement is measured: even this successful campaign is presented with attention to its costs and to the institutional follow-through that made it productive rather than merely destructive.

What is the Tongjian’s view of Wang Anshi’s military reforms?

Sima Guang opposed the reforms that increased military spending. The Tongjian implicitly supports his position by showing, across centuries, that military expansion without fiscal and institutional preparation produces more problems than it solves. The work does not directly address Song-era policy but clearly favors cautious institutional investment over rapid military expansion.

Can the institutional cost of war be mitigated?

The Tongjian shows one method that partially works: keeping military campaigns time-limited and restoring civilian oversight immediately afterward. Emperor Taizong did this after his Turk campaign. Emperor Wu of Han did not, allowing his generals to remain in command indefinitely. The difference in long-term outcomes is clear in the Tongjian‘s parallel treatment of the two reigns.