Mormon sees the world as a reflection of its spiritual relationship to God. Therefore, when the Lamanites are set to come again to battle, he sees it as a failure of his people to turn to the Lord. For Mormon, this would have been a nearly assured result of the inability of his people to turn to the Lord.
Social: The canons of warfare in Mesoamerica did allow for situations such as described here, where the combatant sends notice that of their intent. This was the ideal in Aztec warfare, but the practice seldom extended to the formal announcement to the enemy by that time. (Ross Hassig. Aztec Warfare. University of Oklahoma Press, Norman. 1988, p. 48).
Chronological: the three hundred and sixtieth year would be 350 A.D.