Three times Shiz attacked Coriantumr on the hill Comnor, but suffered such heavy losses that, in spite of the fact that he had wounded Coriantumr severely, Shiz commanded his people that they should not pursue the armies of Coriantumr" (Ether 14:29-31). In the next few verses, Moroni gives the reader an idea as to just how heavy those losses might have been. In Ether 15:2 we find a remarkable number of "nearly two millions of [Coriantumr's] people" being slain in battle.
According to Hugh Nibley, there are a number of examples in ancient history which parallel such massive destruction as that which took place with the Jaredites. When Genghis Khan overcame the great Merkit nation, which was his great rival through all of central Asia, he left only one man alive . . . Incidentally, the wars of Genghis Khan cost China alone 40 million lives. . . . The Assyrian kings, like the Romans, flooded the sites of cities they destroyed to convert them into uninhabitable wastelands. In cities of a million inhabitants, the Mongols left not a dog or a cat alive, and they converted vast provinces to complete deserts. . . . The Kin and the Hsia Hsia were two Hunnish tribes and the two greatest empires of their day, as closely related in blood as were the people of Shiz and Coriantumr. They engaged in 15 years of warfare which wiped out 18 million people--a figure that makes Ether's 2 million people (Ether 15:2) seem rather paltry. Two million were killed in the last extermination. [Hugh W. Nibley, Teachings of the Book of Mormon, Semester 4, pp. 262-263] [See the commentary on Mormon 6:10-15]