Mosiah 9:16 - 9:19
Mosiah 9:16 And it came to pass that I did arm them with bows, and with arrows, with swords, and with cimeters, and with clubs, and with slings, and with all manner of weapons which we could invent, and I and my people did go forth against the Lamanites to battle.
King Zeniff armed all of his people and they in turn attached the Lamanites. They were not armed at the time of the initial attached by the Lamanites but they now had weapons to defend themselves such as swords, cimeters, clubs slings and whatever thing they could use as a weapon. [Don’t know what a cimeter is]
Mosiah 9:17 Yea, in the strength of the Lord did we go forth to battle against the Lamanites; for I and my people did cry mightily to the Lord that he would deliver us out of the hands of our enemies, for we were awakened to a remembrance of the deliverance of our fathers.
Their allay against the Lamanites was the Lord. The people had prayed for the power to defend themselves against the Lamanite aggression. The Nephites remembered that the Lord had delivered their ancestors on various occasions, so they prayed that He would do so now.
Mosiah 9:18 And God did hear our cries and did answer our prayers; and we did go forth in his might; yea, we did go forth against the Lamanites, and in one day and a night we did slay three thousand and forty-three; we did slay them even until we had driven them out of our land.
The Lord responded positively and they were strengthened by an invisible hand. In a battle lasting but one whole day, the Nephites killed 3,043 Lamanites. The fight lasted until the Lamanites withdrew from Nephite lands. [The Nephites did not pursue them into their territory. It was the policy that they would only defend themselves not engage in reprisals on their enemies lands. I think the Lord wanted the people to know about His power of protection, not of His power to punish. That is strictly up to Him personally not for man.]
Mosiah 9:19 And I, myself, with mine own hands, did help to bury their dead. And behold, to our great sorrow and lamentation, two hundred and seventy-nine of our brethren were slain.
King Zeniff counted 279 of his own people killed in the fighting after he had helped bury the Lamanite dead.