outlawed private mints. Wang Mang's regime introduced a variety of new, lightweight currencies, including archaic knife money, which devalued coinage. The wushu coin was reinstated in 40 CE by the founder of Eastern Han, Emperor Guangwu, and remained the standard coin of China until the Tang dynasty. Trade with foreign nations on a large scale began during the reign of Emperor Wu, when he sent the explorer Zhang Qian to contact nations west of China in search of allies to fight the Xiongnu. After the defeat of the Xiongnu, however, Chinese armies established themselves in Central Asia and the Western Regions, starting the famed Silk Road, which became a major avenue of international trade. Xin dynasty In 8 CE, the Han chancellor Wang Mang usurped the throne of the Han emperors and established his own dynasty, the Xin. Wang Mang wanted to restore the Han to what he believed to be the "idyllic" condition of the early Zhou. He outlawed the trading of land and slaves, and instituted numerous state monopolies. These ultra-modernist policies proved highly unpopular with the population, who overthrew and executed him in 25 CE and restored the Han dynasty. Eastern Han dynasty Under the Eastern Han dynasty, which followed Wang Mang's overthrow, earlier laissez-faire policies were reinstated, and the government abolished conscription and withdrew from managing the economy. A new period of prosperity and intellectual thought, called the Rule of Ming and Zhang, began. This period saw the birth of the great scientist, Zhang Heng, and the invention of paper. However, by the end of the 2nd century, Han society began to disintegrate. In 184, a peasant preacher started a rebellion called the Yellow Turban Rebellion, which ended the Han dynasty in all but name. Wei and Jin (220–304) Also known as the Three kingdoms period, the Wei and Jin eras, which followed the collapse of the Han Dynasty, saw large-scale warfare envelop China for the first time in more than 150 years. The death toll and subsequent economic damage were significant. Powerful aristocratic landowners offered shelter to displaced peasants, using their increased authority to reclaim privileges abolished during the Qin and Han. These refugees were no longer taxable by the state. During the Jin, the taxable population was 20 million; during the Han it had been 57 million. Most of North China was unified by Cao Cao, who founded the Wei Dynasty (220–265), and the