The principle reason is not corruption, but usurper no matter succesfully or not. The official in Han was elected from the bottom up to court. So, kind of Confucious ideaology. However, there is a fact that among 13 emperors of the Eastern Han Dynasty, only two of them got the throne when they had grown up. Others are all baby emperors. So, their mother, the emperess and relatives from monther side will help reign the country till the emperor became adult. When the emperors grew up, they wanted to get their authority back. Conflicts would happened. So, some people say that Han is strong but declined for inner risks.