Alma 53:11

and because of their oath, they had been kept from taking up arms against their brethren: for they had taken an oath, that they never would shed blood more; and according to their oath, they would have perished; yea, they would have suffered themselves to have fallen into the hands of their brethren, had it not been for the pity and the exceeding love which Ammon and his brethren had had for them;

Because of their promise, they didn’t fight against their brothers. They promised they would never kill anyone again. They would have kept their promise and died. They would have let their brothers kill them. But Ammon and his brothers loved them very much and felt sorry for them.

Because of their oath, they’d been kept from taking up weapons against their brothers. They had sworn never to shed blood again, and according to that oath, they would have died rather than fight. They would have let themselves fall into enemy hands if Ammon and his brothers hadn’t felt such deep pity and love for them.