Under the fubing, the power of the aristocracy was curbed and shifted to a militia of peasant-soldiers, who were tied to the land that they worked.
Normally they acted as farmers, but could be mobilized in times of war.
Not all troops were primarily farmers.
Some 20% were regular troops who rotated between farming and military duty at their provincial capital.
Those who lived 250 kilometers from the capital served 1 in 5 months, and those over 1,000 kilometers away served 2 in 9 months.
Officers were part of the permanent armed force.
The fubing system was first used by general and later emperor Yuwen Tai of the Western Wei dynasty / state, around 555 CE.
Three decades later emperor Wen re-united China and founded the Sui dynasty.
He adopted the fubing for all of the country and placed it under local administration.
The Sui dynasty was short-lived but many of its changes, like the equal-field system, support for buddhism, standard coinage, examinations for civil servants and also the fubing, survived.
Its successor the T'ang dynasty only tightened central control of the militia.
At its height the T'ang fubing could theoretically field some 600,000 men, mostly in northern China.
The cost of the fubing system for the government was low, but its militia soldiers were unsuitable for long and hard campaigns.
Therefore, starting in the late 7th century CE, it was gradually replaced by a standing army of professional warriors.
War Matrix - Fubing
Dark Age 480 CE - 630 CE, Armies and troops