One of the major political causes of the collapse of the Han Dynasty was the series of purges that it carried out in attempts to suppress challenges to the Han emperors.
As the dynasty's power declined, there arose a number of attempts, often by the relatives of empresses, to take power from the emperors. The emperors tended to meet these efforts with large-scale repressiosn of those who supported the rebellions. These purges led to a great deal of dissatisfaction within the elites of the society.
Another problem was the fact that the largest of the politically powerful families were simply too big to be controlled by the central government. As the emperors lost power, these powerful families took more power for themselves. They were eventually able to split the empire into three separate empires. This was a major step towards the total disruption of the Han Dynasty.