Han dynasty funded wars by monopolizing salt and iron

Two decades of campaigns against the Xiongnu under Emperor Wu of Han had drained the treasury his predecessors had built up, and by the 120s BCE the state faced recurring deficits that outright land-tax increases could only address at serious political cost — peasants directly felt every rise in the land tax, and it was the one lever every subject was already watching.

Salt and iron production, by contrast, was largely in the hands of private magnates who had grown wealthy supplying two goods every household needed regardless of price: salt to preserve and season food, iron for tools and farm implements. Nobody was watching that margin, and nobody could simply stop buying either good if its price crept upward under new management.

On minister Sang Hongyang's design, the state took over salt and iron production and sale as a formal monopoly beginning around 120 BCE, eventually running roughly 35 salt offices across 27 commanderies and at least 48 iron offices across 40 commanderies and kingdoms — extracting revenue through the resale margin on two inelastic necessities instead of touching the land tax rate at all.

Monopolized salt and iron, capturing the resale margin on inelastic necessities so revenue rose invisibly, without touching the land tax everyone watched.

Salt and iron are inelastic necessities, so demand stays high even with price increases.

Revenue embedded in product prices is less visible than an itemized tax line.

The state captured margins previously going to private producers, increasing revenue without raising the land tax.

The policy's invisibility reduced political backlash, allowing it to persist even after its architect's death.

When raising visible prices risks backlash, find a must-have add-on or input and take your cut there, where it's less noticed.

The monopoly became a major and durable revenue source for the Han state, funding continued military campaigns without a corresponding rise in the politically visible land tax, and outlived Sang Hongyang himself — who was executed in 80 BCE amid factional politics — with the policy continuing largely unchanged through the rest of the Western Han period.