Nephi saw it (1 Nephi 12:12-23). Alma saw it too. They both foresaw the entire destruction of the people of Nephi … an entire nation extinct. First came the pride and then they did not believe in Jesus Christ and then came the wars and pestilences and famines and bloodshed until they were finally wiped out.
“Thus saith the Lord God – Cursed shall be the land, yea, this land, unto every nation, kindred, tongue, and people, unto destruction, which do wickedly, when they are fully ripe; and as I have said so shall it be; for this is the cursing and the blessing of God upon the land, for the Lord cannot look upon sin with the least degree of allowance.” (Alma 45:16)
Alma the Younger
Alma’s influence on the Nephites and Lamanites would be felt for years and years to come. His unwavering efforts brought thousands to repentance and to their God. Just as Nephi of old, he saw the destruction of the Nephites. Knowing as they knew, they still persisted in delaying that complete destruction for as long as possible. They did all they could to keep the flame of the Gospel alive in their posterity for as long as they could.
Sadly, Alma 45 ends with these words, “they grew proud, being lifted up in their hearts, because of their exceedingly great riches; therefore they grew rich in their own eyes, and would not give heed to their (Helaman and his brethren) words, to walk uprightly before God.”
It is no coincidence that Moroni put Alma’s prophecy and the words to the cursing and blessing on the land in the same chapter. I think he did that to drive home the point that they were true. As the Nephites grew in pride and riches, they forgot God and then came the famines and wars which would comprise of the war chapters.