Historians typically consider the following dynasties to have unified China proper: the Qin dynasty
The Qin dynasty or Ch'in dynasty was the first dynasty of Imperial China, lasting from 221 to 206 BC. Named for its heartland in Qin state, the dynasty was founded by Qin Shi Huang, the First Emperor of Qin.
Qin Shi Huang began a militarily-driven expansionist policy. In 229 B.C., the Qin seized Zhao territory and continued until they seized all five Zhou states to create a unified Chinese empire in 221 B.C.