Why such a vast country as China has only one civilization while European Union has more civilization?

In certain sense, there're 56 different ethnic groups or civilizations within China. The characteristics and uniqueness of each and different ethnic groups have never been "stopped". Throughout thousands years of history they simply unified as one, somewhat similar to the European Union. It's interesting to see that all the dynastys followed their predecessors in the form of govt systems and methods of ruling hence enabling the cultures and the written language be ped down from generations to generations. Perhaps given more time and development, European Union will become one single entity as the US.