Historical China was a world leader in science and technology until the Ming Dynasty. Ancient Chinese discoveries and inventions, such as papermaking, printing, the compass, and gunpowder (the Four Great Inventions), later became widespread in Asia and Europe. Chinese mathematicians were the first to use negative numbers.[333][334] However, by the 17th century, the Western world had surpassed China in scientific and technological development.[335] The causes of this Great Divergence continue to be debated.[336] After repeated military defeats by Western nations in the 19th century, Chinese reformers began promoting modern science and technology as part of the Self-Strengthening Movement. After the Communists came to power in 1949, efforts were made to organize science and technology based on the model of the Soviet Union, in which scientific research was part of central planning.[337] After Mao's death in 1976, science and technology was established as one of the Four Modernizations,[338] and the Soviet-inspired academic system was gradually reformed.[339]