Question

what caused the han dinasty to fall?

Answer 1

There were a number of reasons, but the one that helped set the stage was the increased power of the regional "inspectors" who administered regions within the empire. They were allowed to levy taxes and maintain their own armed forces within their areas which gave them tremendous influence and would cause no end of problems later on.

Eventually, one of these "warlords" (Dong Zhuo) would seize the throne itself and rule from behind the scenes. After his death, and his brutal reign of terror, things only became worse as other warlords asserted their claims to power. The last emperor of the Han dynasty was forced out of office by the son one one of the warlords (Cao Cao), ending their rule and beginning what China refers to as the Three Kingdoms -- each once part of the empire now headed by the most powerful warlords in each region as they fought to unify the country under their respective flags.