How did the ancient China's Qin state become so powerful that it could unify the entire China?

The Qin state was only one of many small states in the Shang Dynasty period, and the Qin state was a vassal state of the Zhou Dynasty which succeeded the Shang, but the Qin state rapidly grew in power and finally unified all the states in the Warring States period and created the Qin Dynasty. <br><br>How did the Qin state become so powerful that it could unify all the other states?