When Mormon has used “contention” (at least, as translated by Joseph), he means internal dissent, in contrast to war. In the past, religious contention has led to schisms. Here Mormon not only tells us that there are no contentions but also adds that Jesus’s disciples worked “mighty miracles.” The presence of miracles indicates faith and unity, the opposite of divisive contentions. Like Mormon’s other descriptions, this is a generalization, not specific information.