well as on foreign trade, are held by some scholars as a cause of the Great Divergence, by which the Western world overtook China economically. During the Ming–Qing period (1368–1911) the biggest development in the Chinese economy was its transition from a command to a market economy, the latter becoming increasingly more pervasive throughout the Qing's rule. From roughly 1550 to 1800 China proper experienced a second commercial revolution, developing naturally from the first commercial revolution of the Song period which saw the emergence of long-distance inter-regional trade of luxury goods. During the second commercial revolution, for the first time, a large percentage of farming households began producing crops for sale in the local and national markets rather than for their own consumption or barter in the traditional economy. Surplus crops were placed onto the national market for sale, integrating farmers into the commercial economy from the ground up. This naturally led to regions specializing in certain cash-crops for export as China's economy became increasingly reliant on inter-regional trade of bulk staple goods such as cotton, grain, beans, vegetable oils, forest products, animal products, and fertilizer. Silver Silver entered in large quantities from mines in the New World after the Spanish conquered the Philippines in the 1570s. The re-opening of the southeast coast, which had been closed in the late 17th century, quickly revived trade, which expanded at 4% per annum throughout the latter part of the 18th century. China continued to export tea, silk and manufactures, creating a large, favorable trade balance with the West. The resulting expansion of the money supply supported competitive and stable markets. During the mid-Ming China had gradually shifted to silver as the standard currency for large scale transactions and by the late Kangxi reign the assessment and collection of the land tax was done in silver. Landlords began only accepting rent payments in silver rather than in crops themselves, which in turn incentivized farmers to produce crops for sale in local and national markets rather than for their own personal consumption or barter. Unlike the copper coins, qian or cash, used mainly for smaller transactions, silver was not reliably minted into a coin but rather was traded in units of weight: the liang or tael, which equaled roughly 1.3 ounces of silver. A third-party had to be brought in to assess the weight and purity of the silver, resulting in an extra "meltage