Did the former Qin Dynasty ever unify China, and then why did it split?

It can only be said that the former Qin dynasty once unified the northern region. Later, with the failure of the Battle of Feishui, other ethnic groups originally belonging to the former Qin Dynasty took the opportunity to become independent, and the north fell into a state of division. In addition, the pre-Qin period belonged to the Sixteen Eastern Countries, from 304 when Xiongnu nobles established the Han State to 439 when Xianbei Tuoba unified the North.