why did the three kingdoms end?

This is a trend. In Chinese history, unification and separation happened alternately. There were reason from many aspect to cause the end of the three kingdoms. Successors were imcapable, especially the foolish Liu Chan of Shu Kingdom. The other important reason is Liu Bei launched the eastward aggressions broke the ally relationship with Wu. Compared with Wei Kingdom, Shu and Wu were weaker. They used to be partner to against Wei together. Once there was a fight between Shu and Wu, Wei had the chance to defeat both of them. There was a intestine strife in Cao Cao's family. Si Ma Family (as the general) got stronger and in charge of the authority. To follow as a matter of course, a new dynasty established by Si Ma Yan, Jin Dynasty came finally.

three kingdoms ended because of of the sima clan that became from the wei sima yi had other plans then when his cam along sami yi yougest son, son started a new era and took all the kingdoms