Alma 3:14

Thus the word of God is fulfilled, for these are the words which he saith to Nephi: Behold, the Lamanites have I cursed; and I will set a mark upon them, that they and their seed may be separated from thee and thy seed, from this time henceforth and forever, except they repent of their wickedness and turn to me, that I may have mercy upon them.

This is how God’s word came true. These are the words he said to Nephi: “I have cursed the Lamanites. I will put a mark on them so they and their children will be separate from you and your children, from now until forever. But if they stop doing wrong and turn to me, I can forgive them.”

In doing this, they fulfilled God’s word without even knowing it. God had told Nephi long ago: “I’ve cursed the Lamanites, and I’ll put a mark on them so they and their descendants will be separated from you and yours forever—unless they turn from their wickedness and come back to me. Then I can show them mercy.”