Mormon Ch4

The wars continue and greater wickedness is over the land than any that has happened before as wicked punish the wicked. Lamanites sacrifice women and children to idols and the Lamanites start winning against the Nephites.
The Nephites attack the Lamanites in 363 but they were driven out and were weary when a fresh army of Lamanites attacked them taking prisoners, slaying many, and only a few were able to flee to the city Teancum (v1-3). The Nephites lost because they weren't on the defensive, the judgements of God will come upon the wicked (aka the Nephites) to be punished by other wicked people (aka the Lamanites), and this is seen even when they are attacked in the year 364 and thousands of lives are lost when the Nephites barely win (v4-9). Then again in year 366, the Lamanites attack and cause an incredibly horrific scene of blood and carnage that the people delighted in and showed that their wickedness was the greatest among any people that their has been on earth (v10-12).
The Lamanites won their battle in Desolation, and attacked Teancum where they took many prisoners, women and children, that they sacrificed to their idol gods which made the Nephites mad and they attacked in great anger driving the Lamanites out of the land (v13-15). It wasn't until 375 that the Lamanites came against the Nephites, beating them in Desolation and then in Boaz because they fought with all their power and desire to slaughter the race of Nephites (v16-21). In each instance, the Nephites could not win and had to flee out of their towns and villages, and Mormon even had to gather the records so they would not be overtaken when the Lamanites came (v22-23).