By the middle of the Tang dynasty (618-907) the system of equalized landholding administered by the ruler had seriously deteriorated. As a result the government found difficulty in collecting taxes and there was less revenue for the state. In the eighth century Yang Yen, a high-ranking official, expressed concerns over the growing financial crisis in a memorial to the Tang emperor:

When the dynastic laws were first formulated there was the land tax, the labor tax on able-bodied men, and the cloth tax on households. But enforcement of the law was lax; people migrated or died, and landed property changed, hands. The poor rose and the rich fell. The Board of Revenue year after year presented out-of-date figures to the court. Those who were sent to guard the frontiers were exempted from land tax and labor tax for six years, after...