The collapse of the Han dynasty was followed by nearly four centuries of rule by warlords. The age of civil wars and disunity began with the era of the Three Kingdoms (Wei, Shu, and Wu, which had overlapping reigns during the period A.D. 220-80). In later times, fiction and drama greatly romanticized the reputed chivalry of this period. Unity was restored briefly in the early years of the Jin dynasty (A.D. 265-420), but the Jin could not long contain the invasions of the nomadic peoples. In A.D. 317 the Jin court was forced to flee from Luoyang and reestablished
itself at Nanjing to the south. The transfer of the capital coincided with China's political fragmentation into a succession of dynasties that was to last from A.D. 304 to 589. During this period the process of sinicization accelerated among the non-Chinese arrivals in the north and among the aboriginal tribesmen in the south. This process was also accompanied by the increasing popularity of Buddhism (introduced into China in the first century A.D.) in both north and south China. Despite the political disunity of the times, there were notable technological advances. The invention of gunpowder (at that time for use only in fireworks) and the wheelbarrow is believed to date from the sixth or seventh century. Advances in medicine, astronomy, and cartography are also noted by historians.