13 And it came to pass that the Lamanites did take possession of the city Desolation, and this because their number did exceed the number of the Nephites.
14 And they did also march forward against the city Teancum, and did drive the inhabitants forth out of her, and did take many prisoners both women and children, and did offer them up as sacrifices unto their idol gods.
15 And it came to pass that in the three hundred and sixty and seventh year, the Nephites being angry because the Lamanites had sacrificed their women and their children, that they did go against the Lamanites with exceedingly great anger, insomuch that they did beat again the Lamanites, and drive them out of their lands.
16 And the Lamanites did not come again against the Nephites until the three hundred and seventy and fifth year.
17 And in this year they did come down against the Nephites with all their powers; and they were not numbered because of the greatness of their number.
18 And from this time forth did the Nephites gain no power over the Lamanites, but began to be swept off by them even as a dew before the sun.
(Book of Mormon | Mormon 4:13 - 18)
The Lamanites win a few battles and believing in a higher power, albeit the wrong one, they offer up human sacrifices to their idol gods. The Nephites are enraged and fight back with great ferocity. So much so, that they drive the Lamanites back out of their lands.
Throughout the Book of Mormon it always appears that the Lamanites were more numerous than the Nephites. This is mentioned several times during conflict, see Jarom 1:6, Mosiah 20:11, Mosiah 25:3, and Alma 2:24-35.
In times past, the greater number of Lamanites caused the Nephites to turn to the Lord for protection. They were put into a situation where they needed to rely on Him or be destroyed. In the past, they eventually turned to Him who is mighty to save. Unfortunately, at this time they are too far gone. They are past feeling, meaning they couldn’t feel the promptings of the Holy Spirit encouraging them to repent and be saved.
Sometimes it may seem that our challenges and trials are overwhelming and too great for us to handle. It is in these difficult times that we need to turn to a loving Heavenly Father who gives weakness unto us that we might humble ourselves before him. His grace is sufficient when are mere mortal strength is not enough to save us.