For years I’ve assumed that when the Lord warned King Mosiah I in a dream to take his people and flee northward (Omni 1:12) that it was on account of a massive Lamanite invasion.
However, I was often then confused by an event happening less than 100 years later. We find that Zeniff goes back to the first inheritance Land of Nephi. His group is led by a violent man, who upon seeing the few Lamanites that have actually moved into the area, chooses to destroy them and take the land by violence. Zeniff fights him, and returns to Zarahemla to pick up replacements to peacefully settle the Land of Nephi. Being that the area is not wholly settled by Lamanites, the Lamanite king allows them to move in and take up residency, while moving the few Lamanites out of the area. (Mosiah 1)
This does not sound like the Land of Nephi was invaded. If it had been, one would think there would be large numbers of Lamanites dwelling in the land when Zeniff appeared 70-100 years later.
So, what could have been the reason for the sudden flight by Mosiah and his people? Recently rereading a great book on archaeology and history, “Gods, Graves and Scholars” by C.W. Ceram, the portion on the Maya noted an event where the entire Maya civilization left suddenly, leaving behind their great temples, etc. There is no archaeological evidence of battles, or any people dwelling there after the quick departure. Instead, the entire place was left to be swallowed up by the jungle for over a thousand years. The Maya only moved a few hundred miles away, so events such as climate change did not occur. There is no evidence of earthquakes destroying the place.
So, what do the archaeologists believe probably happened? While the Maya developed great skills in temple building, writing, and jade jewelry, they never spent the time to develop the plow or agricultural methods. They used slash and burn techniques. They would burn down a section of the forest, then plant maize, one hole at a time. After a few years, the soil would be depleted, and they would burn down another section of forest and do the same thing. After a few centuries, the distance to travel to the fields from the cities would be too far to maintain civilization. So the entire group moved north. This would allow the land to recover over decades.
Many Maya cities are built upon previous Maya cities, sometimes 5 levels deep. It is possible that some of these were from the peoples returning back to sites previously used, where the fields were worn out, and then allowed to remain fallow for decades or even centuries before returning.
And this is possibly a reason why the Nephites under Mosiah also fled. The Lord could have warned him concerning crop failure and famine if the Nephites were to stay in the land of Nephi. Zeniff and his people could plan a return to the Land of Nephi without wondering how to overcome a massive group of Lamanites in the area, because they knew the land had to remain fallow for a few generations before being habitable again.