Helaman requests that the Lord send a famine instead of their usual punishment. It seems that Nephi's idea is a good one. The Nephites had likely gotten used to warfare as it was so commonplace among them. The famine had a greater effect in bringing the people to a repentant and humble state. This may be because the Nephites had never before experienced a famine. When Lehi's family arrived, they described a land which was rich and fertile so that their crops 'did grow exceedingly' (1 Nephi 18:24). Ever since their arrival in the New World, the land had been consistently productive.
"Famine is one of heaven's most eloquent sermons. When virtually all else has failed to get the attention of the rebellious and turn them to God, famines have succeeded. Famines can strip men of every sense of self-sufficiency and turn their eyes and ears to the voice of heaven. (See Isaiah 51:19; Jeremiah 14:13-18; Amos 4:6.) In this story it seems that Nephi felt that the people simply did not see the connection between devastating war and their sinful ways." (McConkie and Millet, Doctrinal Commentary on the Book of Mormon, vol. 3, p. 390)