"... one of the greatest achievements of Chinese civilization". Although it began as a despotic regime, the Ming government evolved into a system of power-sharing between the emperor and the civil service. The Ming government collected far less revenue than the Song dynasty. Regional tax quotas set up by the Emperor Hongwu would be collected, though in practice Ming revenues were markedly lower than the quotas declared. The gentry class won concessions from the government and resisted tax increases. Throughout the Ming dynasty, the state was constantly underfunded. Unlike earlier dynasties such as the Tang and Song, and later dynasties such as the Qing, the Ming did not regulate the economy, but had a laissez-faire policy similar to that of the Han dynasty. The Cambridge history of China volume on the Ming Dynasty stated that: Ming government allowed those Chinese people who could attain more than mere subsistence to employ their resources mostly for the uses freely chosen by them, for it was a government that, by comparison with others throughout the world then and later, taxed the people at very low levels and left most of the wealth generated by its productive people in the regions where that wealth was produced. Key Ming taxes included the land tax (21 million taels), the service levy (direct requisitioning of labour services and goods from civilians, valued at about 10 million taels), and the revenue from the Ming salt monopoly (2 million taels). Other miscellaneous sources of revenue included the inland customs duty (343,729 taels), sale of rank (500,000 taels), licensing fees for monks (200,000 taels), and fines (300,000 taels) and others, which all added up to about 4 million taels. The overall Ming tax rate was very low, at around 3 to 4%. However, by the end of the dynasty, this situation had changed dramatically. Zhang Juzheng instituted the single whip law, in which the arbitrary service levy was merged into the land tax. The Ming government's salt monopoly was undermined by private sellers, and had collapsed completely by the 15th century; government officials estimated that three-quarters of salt produced was being sold privately. Ming commerce and currency Zhu Yuanzhang had promoted foreign trade as a source of revenue while he was a rebel, but sharply curtailed this with a series of sea bans (haijin) once in power. These proclaimed the death penalty for private foreign traders and exile for their