Han Empire/Dynasty:
-By the 180s the Han court had grown weak, with debauched or disinterested emperors who lived only for amusement. Court eunuchs vied for power with the scholar-officials and army generals, at times even leading to massacres within the palace. In 189 CE, the warlord Dong Zhuo went so far as to assassinate the 13-year-old Emperor Shao, placing Shao's younger brother on the throne instead.
- One reason that the peasants fled at the rumor of tax collectors is that they were trying to survive on smaller and smaller plots of farm land. The population was growing quickly, and each son was supposed to inherit a piece of land when the father died. Thus, farms were quickly being carved into ever-tinier bits, and peasant families had trouble supporting themselves, even if they managed to avoid paying taxes.
- One of the most important factors in the collapse of the Han Dynasty, in fact, may have been the Sino-Xiongnu Wars of 133 BCE to 89 CE. Over more than two centuries, the Chinese and the Xiongnu fought throughout the western regions of China - a critical area that Silk Road trade goods had to cross to reach the Han Chinese cities. In 89 CE, the Han crushed the Xiongnu state, but this victory came at such a high price that it helped to fatally destabilize the Han government.
Source: http://asianhistory.about.com/od/ancientchina/f/Why-Did-Han-China-Collapse.htm
The Roman Empire:
- The invading army reached the outskirts of Rome, which had been left totally undefended. In 410 C.E., the Visigoths, led by Alaric, breached the walls of Rome and sacked the capital of the Roman Empire. The Visigoths looted, burned, and pillaged their way through the city, leaving a wake of destruction wherever they went. The plundering continued for three days. For the first time in nearly a millennium, the city of Rome was in the hands of someone other than the Romans. This was the first time that the city of Rome was sacked, but by no means the last.
- There were political and military difficulties, as well. It didn't help matters that political amateurs were in control of Rome in the years leading up to its fall. Army generals dominated the emperorship, and corruption was rampant. Over time, the military was transformed into a mercenary army with no real loyalty to Rome. As money grew tight, the government hired the cheaper and less reliable Germanic soldiers to fight in Roman armies. By the end, these armies were defending Rome against their fellow Germanic tribesmen. Under these circumstances, the sack of Rome came as no surprise.
- Other fundamental problems contributed to the fall. In the economically ailing west, a decrease in agricultural production led to higher food prices. The western half of the empire had a large trade deficit with the eastern half. The west purchased luxury goods from the east but had nothing to offer in exchange. To make up for the lack of money, the government began producing