1279, the Black Plague in the 14th century, and the large-scale rebellions that followed it, China's population was buoyed by the Columbian Exchange and increased greatly under the Ming (1368-1644 AD/CE). The economy was remonetised by Japanese and South American silver brought through foreign trade, despite generally isolationist policies. The relative economic status of Europe and China during most of the Qing (1644-1912 AD/CE) remains a matter of debate, but a Great Divergence was apparent in the 19th century, pushed by the Industrial and Technological Revolutions. Pre-imperial era By Neolithic times, the tribes living in what is now the Yellow River valley were practising agriculture. By the third millennium BCE, stratified Bronze Age societies had emerged, most notably the Erlitou culture. The Erlitou dominated northern China and are identified with the Xia dynasty, the first dynasty in traditional Chinese historiography. Erlitou was followed by the Shang and Zhou dynasties, which developed a manorial economy similar to that of medieval Western Europe. By the end of the Spring and Autumn period, this system began to collapse and was replaced by a prosperous economy of self-sufficient farmers and artisans during the Warring States period. This transformation was completed when the state of Qin unified China in 221 BCE, initiating the imperial era of Chinese history. Neolithic and early Bronze Ages Agriculture began almost 10,000 years ago in several regions of modern-day China. The earliest domesticated crops were millet in the north and rice in the south. Some Neolithic cultures produced textiles with hand-operated spindle-whorls as early as 5000 BCE. The earliest discovered silk remains date to the early third millennium BCE. By Northern China's Longshan culture (3rd millennium BCE), a large number of communities with stratified social structures had emerged. The Erlitou culture (-1350 BCE), named after its type site in modern Henan, dominated northern China in the early second millennium BCE, when urban societies and bronze casting first appeared in the area. The cowries, tin, jade, and turquoise that were buried at Erlitou suggest that they traded with many neighbours. A considerable labour force would be required to build the rammed-earth foundations of their buildings. Although the highly stratified Erlitou society has left no writing, some historians have identified it as the legendary Xia dynasty mentioned in traditional Chinese accounts as preceding the Shang. Only a strong centralised state led by rich elites could have produced the bronzes of the Erligang