Helaman 4:24-26
24.  And they saw that they had become weak, like unto their brethren, the Lamanites, and that the Spirit of the Lord did no more preserve them; yea, it had withdrawn from them because the Spirit of the Lord doth not dwell in unholy temples–
25.  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 more exceeding numerous than they, and except they should cleave unto the Lord their God they must unavoidably perish.
26.  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; yes, thus had they become weak, because of their transgression, in the space of not many years.