The Song period (960-1279 AD/CE) brought additional economic reforms. Paper money, the compass, and other technological advances facilitated communication on a large scale and the widespread circulation of books. The state's control of the economy diminished, allowing private merchants to prosper and a large increase in investment and profit. Despite disruptions during the Mongol conquest of 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.