It is 190 CE. Central authority has collapsed and nine provinces answer to nobody. You hold one of them. The obvious move is to raise an army and take the rest — and it is the move that destroys you, because your writ reaches exactly as far as your grain does. Free in the browser, no install and no account.
Pre-modern conquest was a logistics problem wearing a military costume. Grain here is a network, not a number: it spreads outward from your garrison farms one province per year and loses nearly half its value at every step. March beyond that gradient and your host deals a fraction of its damage while taking several times the losses. That is Guandu and Red Cliffs expressed as arithmetic rather than anecdote.
GARRISON FARMS (tuntian) — Cao Cao adopted the system in 196 CE, settling refugees and surrendered Yellow Turbans on state land under military supervision. The first year around his capital reportedly yielded a million hu of grain, which is why his armies could still campaign while his rivals' men were eating mulberries and river snails.
GOVERN — Han provinces ran on centrally appointed Inspectors and Grand Administrators working with local great families. Holding a province meant reconstituting that machinery, not garrisoning it. Order decays every year you neglect it.
LEVY — armies came from the households of the provinces you held, so every soldier raised was a pair of hands taken off the land that fed him. An army is a claim on grain, not a free asset.
MARCH — effective strength scales with the supply reaching the target province, and your casualties scale inversely. At Guandu in 200 CE, Cao Cao burned Yuan Shao's depot at Wuchao and the larger army disintegrated within days. The battle was decided at the granary.
SUMMON TO COURT — a province that submits keeps its officials, its records and its harvest. One taken by storm loses all three and must be rebuilt before it yields anything. Persuasion is not the soft option; it is the efficient one.
ESCORT THE EMPEROR — in 196 CE Emperor Xian was escorted from the ruins of Luoyang to Cao Cao's capital, making every command an imperial edict and every enemy a rebel. Ju Shou urged the same course on the far stronger Yuan Shao, who declined. It is the pivot of the whole game, as it was of the era.
Territory taken faster than it can be administered revolts back out — as it did in 194 CE, when Zhang Miao and Chen Gong handed Yan Province to Lü Bu while Cao Cao campaigned in Xu. Geography did the rest: Yi Province sat behind the Qinling mountains, Yang Province behind the Yangtze and a navy the north did not have. China was not reunified until Jin took Wu in 280 CE, ninety-six years after the Yellow Turbans rose.
One playthrough runs about fifteen minutes. It needs no login, no install and no student accounts — a link is enough. The endings debrief distinct failure modes: losing your home base, conquering faster than you can govern, or simply leaving the realm divided when the clock runs out. The model is deterministic, so a class can replay the same map and compare strategies. Suitable for senior history covering the fall of the Han, Chinese imperial administration, and the logistics of pre-modern warfare.