The phrase “there was no more contention in all the land” typically comes as a conclusion rather than a beginning. It is probable that this really was a concluding sentiment and referred to the lost descriptions of the wars and contentions that king Benjamin had to deal with that were recorded at the end of Words of Mormon.
This verse has an unusual doubling of the idea that there is no contention. The first looks backwards to the resolution of conflict: “And now there was no more contention.” The second looks forward to the end of Benjamin’s reign: “king Benjamin had continual peace all the remainder of his days.” Unlike similar statements in the small plates, this foreshadowing cannot tell us anything about when the original book of Mosiah was written. The phrase is Mormon’s, and Mormon clearly wrote long after the events.
Why would Mormon double this idea of a lack of contention? We can understand it best if we remember the promise of the land. Righteousness and safety, or peace, go hand-in-hand. Mormon is telling his readers that king Benjamin was righteous. He defeated contentions and wars, and that ushered in not only a righteous people, but also a peaceful time.
The next reason for the peace will be demonstrated in the event that Mormon elected to describe next, which was the gathering of the people of Nephi in Zarahemla for a major discourse from the king to all of his remaining people.