After Ji Chang declared himself a king, he was going to defeat the Shang Dynasty. Consequently, he invited many vassals to suppress the Shang Dynasty together, but they all declined out of fear for the atrocity of King Zhou and the mighty power of Shang Dynasty. They chose to watch from a distance and help the side which was about to win. This was just a way to secure their safety.
Although Ji Chang did not obtain the support of other vassals, suppressing the Shang Dynasty was unavoidable. In the court, he discussed with his officials which person was most qualified to be a general to lead the attack against the Shang Dynasty. Both Bo Yikao and Ji Fa were willing to be the general, which gave Ji Chang a headache. Either of them would gain significant benefits if they made contributions on the battlefields. How could they give up?
