Coriantumr was driven to repentance, but his wish to stop the bloodshed and save his people was ultimately frustrated not by his wish to change but by the depravity of the people. They were too far gone.
3 He began to repent of the evil which he had done; he began to remember the words which had been spoken by the mouth of all the prophets, and he saw them that they were fulfilled thus far, every whit; and his soul mourned and refused to be comforted.
6 And it came to pass that the people repented not of their iniquity; and the people of Coriantumr were stirred up to anger against the people of Shiz; and the people of Shiz were stirred up to anger against the people of Coriantumr; wherefore, the people of Shiz did give battle unto the people of Coriantumr.
How could a people who had been so blessed become so cold that they would fight until every last one of them was dead? This kind of downward spiral is hard for me to imagine, but people in our time have determined to slaughter innocents in the name of what they consider to be a higher cause. Satan is stirring up the hearts of people to anger so that they accept that killing others is acceptable and even righteous. We need to look to the Savior and pray for his swift return in glory to bring an end to evil and a return to peace.