Because they do not have a stable government, they have experienced many departments internally, and they can not keep order. During this period, China fell into despair and collapse until he had a longer and better emperor.
Historically, once the focus of East Asia - Asian architecture changes from inner Asia to East Asia, there are two consequences. 1) Asian countries seek isolation or autonomy - or "four betrayal" known to the Chinese - "This is a norm for the East Asian regime or reform of the dynasty." 2) The new conqueror is old Swapping conquistadors and establishing new East Asia and Asian empire by invasion Union with Communist Party replaces Manchuria - Mongolia Union
The complex of Neia and East Asia was always the traditional cornerstone of the Asian Empire. Guinea exports organization and technology, East Asia provides human resources and funds. East Asian empires such as Mongolia and Mancos are politically dependent on a few Asian internal organizers and most East Asian tribute payers during the golden era, but this is a coincidence. Military training was also conducted on a few Neiya fighters and most East Asian supplements. Neia's organization and technology which lose human resources and money in East Asia can only preserve traditional tribes and feudal liberties within Asia, but it is impossible to establish and maintain an empire with vast territory and population is enough.