Textual: In contrast to the record of his father, Abinadom writes some time after receiving the plates. The brevity of his text and the brusqueness of the conclusion suggest that he is writing near the end of his life, immediately prior to giving up the plates to his son. I would suggest that his entire message was written in a single sitting, sometime when he realized that he was about to die (which may also account for some of the brevity of the text).
Historical: Abinadom notes that he has seen "much war and contention" between Nephite and Lamanite. While brief, he yet gives us some very important information. The salient ideas are that there was more than one incident, and "much war" suggests more than two or three. In addition, Abinadom notes that he has been a warrior, and taken the lives of Lamanites "in the defense of my brethren." While it is possible that the term "in the defense" might be formulaic, it is more probable that he means it literally, and that the wars being fought are defensive rather than offensive.
Following the logic of the social model that has been described, the Lamanites have made a significant incursion into Nephi in 266BC. In the years following that event, the city of Nephi remains, and is able to rebuild sufficiently to be defensible. At some point their relations with surrounding towns deteriorates, and with the power of their position diminished, they are open to more attack from more peoples.
The wars with the Lamanites do not appear to be large scale military actions, however, as the larger population of the Lamanites suggests that had they been motivated to cooperate and put together a large army they could have overwhelmed the Nephites. This did not happen, and the defensive strategies of the Nephites were successful. This suggests that the military actions where on a smaller scale, and therefore probably related to specific surrounding towns rather than a cohesive Lamanite "country." We must remember, at this point, Jacob's definition that anyone who seeks to destroy the Nephites was a Lamanite (Jacob 1:14). At this point we see no evidence of a "Lamanite" nation. The evidence is much more suggestive of smaller towns or smaller cities who act against the Nephites. A single town or city might not keep up a multiple year war that they keep losing, but multiple towns might try for the same prize, with the result being that the Nephites continually see war, where the losing Lamanites are not as consistently engaged in warfare.
That the Nephites are able to fend on the multiple wars suggests a remaining population that is still fairly large, even after the destruction of the "more wicked part" of the people. They may have also retained technological superiority, although the number of years spent in trade contact with other locations would suggest that the technological basis for superiority would be waning as the other communities learned what the Nephites knew (to the extent that it could be copied - military secrets are usually guarded, even in trade relations).