The First Emperor's father Yiren was the grandson (son of the son) of Ze, the ruler of Qin. The rulers of Qin and Zhao were from the same family, but the two lands fought against one another frequently. They wanted to make peace. King Ze gave his grandson Yiren to the leaders of Zhao so that, if Qin started to fight Zhao, the ruler of Zhao would kill Yiren and his family. Because King Ze would not want that, the ruler of Zhao was able to have less fear that Qin would fight him. (He also sent people from his family as prisoners to Qin so that things were even.)