Social: The problems between the Lamanites and the Noahites begin with small raiding parties. As happened in Zeniff's rule, the attack on this non-Lamanite population came in small raids rather than massive warfare. This is fairly significant because it allows us to make some inferences about the political climate of the time.
First, we should delineate what these attacks were not. They were not an organized and coordinated assault by combined Lamanite armies. The description Mormon gives is clearly much smaller in scale. The raids come upon small numbers of people in the fields. This is not an attack against a political institution, but an attack against goods (and secondarily the people who control them). A successful Lamanite raid would yield goods (crops and flocks) but had no direct effect on the political balance among the various communities. No king was attacked. No city was threatened. The motivation was small, not large.
Noah reacts to these raids appropriately, but not necessarily effectively. He apparently does not consider them to be threats against himself and his rule, but sees them for what they are - robbing bands. He sends out guards, but in insufficient numbers. This again tells us that the marauders are small bands. Garrisons are not sent, but guards. Noah is reacting small to a small threat. Nevertheless, Mormon (possibly influenced by his very personal involvement in Lamanite wars, sees these are very significant events. The raids appear to be more important to Mormon that they were to Noah, based on Mormon's verbal response compared to Noah's physical response. Mormon's purpose is served by indicating an escalation of Lamanite incursions against Noah's people, but it is very possible that the language he uses is colored by his personal experience of over 600 years later.