completely from 1644 to 1683, and it later restricted to only one port at Guangzhou. In addition, commerce had to be conducted by 13 guilds approved by the government, with competition prohibited. The government also refused to provide protection to overseas Chinese. The emperor did not protest the massacres carried out by the Spanish and Dutch colonial authorities against the Chinese, such as what happened in the Spanish Philippines. Restoration of serfdom The restoration of serfdom is cited as another policy that greatly hampered the Chinese economy. Qing forces expropriated huge amounts of land, turning millions of people from tenant farmers into hereditary serfs. The amount of land requisitioned amounted to nearly 16 million mou, or nearly 10,666 km2, of farmland. Serfdom was so common in the early Qing that slave markets were set up to buy and sell those who had been enslaved during the Qing expansion. Literary persecution While literary persecution existed in China prior to Qing rule, it was rare and never widespread. During the late Ming dynasty, protests by scholars forced the government to declare that "speech will not be criminalized". However, the Qing government frequently used literary persecution to destroy opposition to Qing rule. Several cases of literary persecution saw hundreds of intellectuals and their families executed, often for minor offenses such as referring to Manchus as "barbarians" and using the Qing character in areas that was deemed offensive by the government. Thousands of ancient texts deemed subversive were burned in the persecutions. Protests by scholars, which had been common during the late Ming period, were also suppressed. The persecutions extended to non-orthodox thought as well; scholars who disagreed with the standard Neo-Confucian theories were executed along with a scientist who argued that the brain, rather than the heart, was the centre of thought. Domestic intervention The Qing dynasty intervened in the economy far more than its predecessors. Unlike the Ming dynasty, who had adopted laissez-faire policies, there was frequent intervention in the economy by restricting the number of merchants allowed to operate. The official edicts discouraged the cultivation of commercial crops, in favour of subsistence agriculture. Also, most new mines were prohibited. Supporters of the theory claim that such policies greatly damaged the Chinese economy. Devastation of initial conquest The Ming-Qing transition was one of the most devastating wars in Chinese history, and it set back Chinese progress decades. Examples of the devastation include