It quickly expanded , extending the Southern frontier from the Yangtze to modern Vietnam , and the northern frontier to modern Mongolia .
In 221 BCE , the State of Qin conquered the remaining states in China , becoming what scholars consider the first unified Chinese state .
China quickly expanded , extending the Southern frontier from the Yangtze to modern Vietnam , and the northern frontier to modern Mongolia .
In 221 BCE , the State of Qin conquered the remaining states in China , becoming what scholars consider the first unified Chinese state .