The whole land being devasteted by the Mongol ruling elite, by wars and by a corrupt local government, there was the urgent need for a thorough economical reconstruction especially of northern China. Natural deasters in the last years of the Mongol rule had caused suffering to great parts of the population in the Yellow River basin. Fields, dams and canals had to be reconstructed and repaired. Until the end of the 14th century, intensive and huge irrigation and reforestation projects were implemented. The Ming government thus started to rely more on agriculture than on commerce - while the greatest part of tax income during the Song Dynasty was based on commerce and merchandise. To obtain the most possible amount of taxes, an exact population census was necessary. Only in the later part of the Ming period, the census was neglected. According to traditional classification of the populace, and following the Mongol pattern of tax classification, all taxed people belonged lifelong and for generations to exactly one group: soldiers, peasants, or artisans. Their respective taxes were collected by different ministries, either the household ministry, the military ministry, or the ministry for public work. This theoretical framework from the begin of Ming was not possible to be exerted for longer generations. The weakness of later emperors and the central government was reflected in the inability by the local government to collect taxes without relying on the help of the local gentry. The state-implemented definition of a family's economical activities began to dissolve from the begin of 15th century on. Peasant families became victim of the gentry and had to serve them as tenant farmers. Many peasants were so poor that they fled to the pirates, engaged in smuggling and in the forbidden exploiting of mines. The same problem touched the military and artisan families that had to serve the state for salaries less than market prices. The intention of the early Ming government to be free from the task of recruiting peasant soldiers during times of war, had to be given up, and the government turned back to the traditonal recruitment use. State employed artisans - working in state run manufacturies like the porcelain factories of Jingdezhen 景德鎮/Jiangxi - became less and less because they bought themselves free or engaged in private business. Social unrests and rebellions were notorious from the 15th century on, some of them were headed by religious leaders, but most of these rebellions were economically determined, like the miners uprising of Deng Maoqi 鄧茂七 in 1448 and the rebellion of Li Zicheng 李自成 that eventually lead to the end of Ming Dynasty. Song Dynasty officials had developed paper money during the 11th century, long before Western countries introduced paper money. But the Ming Dynasty was the last to make widespread use of paper money: it was not convertible into coins and therewith suffered of gallopping inflation rates. From the 15th century on, silver bars (liang 兩, by the Westerners called tael, a Malay word) began to replace the paper money and served as the usual big currency - apart from the small copper coins - until the end of Qing Dynasty. Silver had to be imported from America, another proof for Chinese navigation techniques, and an example that widespread navigation and commerce did not cease in spite of the piracy attacks in the East China Sea. Ming China was the greatest importing and exporting nation of the 17th century world. The social mobility - forced by the bad economic situations on the countryside - lead to a growing of the cities especially in the lower Yangtze area. Immigrating peasants changed their profession to become merchants, artisans sold their products from small manufacturies in their small shops. Many people from the countryside were also employed in private or state run manufacturies producing paper, porcelain, cotton or silk fabric, or on the pre-indstrial tea, sugar cane and tobacco (introduced from the Americas) plantations. Technical improvements like silk looms and agrarian tools supported the begin of industrialisation in many fields of the Chinese economy. But these developments also lead to the upcoming of a class of rich bankers and finance people as well as that of an urban proletarian population.