1. After a period of disunity following the collapse of the Han Dynasty in AD 220, China was reunified by the Sui Dynasty in AD 581. 2. The Tang Dynasty (AD 618-907) strengthened China by establishing a civil service system based on merit. The capital city of Chang'an became the largest city in the world. 3. The Song Dynasty (AD 960-1279) faced military pressures and moved their capital south to Hangzhou for protection. Confucian philosophy became influential again and Buddhism faced declining support.