We could have just had generic Nephite soldiers but it was nice to include the heroic, young Ammonite warriors. The irony is that pawns have a tendency to get captured constantly which doesn't relate, historically, to the undefeatable Ammonites but pawns also are the only pieces that can turn the tide of the battle by trading themselves in for a mightier piece to take the field. In this selfless way they are a perfect fit.