Moronihah succeeded his father as commander of the Nephite armed forces perhaps around 60 BC. As the son of Moroni, he received superior training from his father—in strategy, leadership, and love of God and liberty. The peace left behind by the retiring Moroni and his colleague Helaman was not long-lasting. Moronihah’s initial battle came when the Lamanites under the Nephite dissenter Coriantumr succeeded in overpowering the capital city of Zarahemla in the year 51 BC in a campaign involving a massive invasion. Moronihah and his general Lehi were able to repel the Lamanites and expel them from the land, Coriantumr having been killed. Peace between the warring nations was restored for a time.
Some years later, in the year 34 BC, Nephite dissenters and their Lamanite allies succeeded once more in taking over the land of Zarahemla and driving the forces of Moronihah upward toward Bountiful. Even after several years of battle, the Nephites were able to regain only half of their lands. According to Mormon, “this great loss of the Nephites, and the great slaughter which was among them, would not have happened had it not been for their wickedness and their abomination which was among them; yea, and it was among those also who professed to belong to the church of God”. Moronihah and Nephi and Lehi, the sons of Helaman, preached repentance to the people, and the people began to respond. Moronihah tried diligently to regain the remainder of the lands and possessions of the people, but his efforts were in vain. The situation had become advantageous to the Lamanites because of the decline in spirituality and faith among the Nephites.
Therefore the Lord did cease to preserve them by his miraculous and matchless power, for they had fallen into a state of unbelief and awful wickedness; and they saw that the Lamanites were exceedingly more numerous than they, and except they should cleave unto the Lord their God they must unavoidably perish.
For behold, they saw that the strength of the Lamanites was as great as their strength, even man for man. And thus had they fallen into this great transgression; yea, thus had they become weak, because of their transgression, in the space of not many years.