Alma 2:10

Now when Amlici was made king over them, he commanded them that they should take up arms against their brethren; and this he done, that he might subject them to him.

After Amlici became their king, he told them to fight against their brothers. He did this because he wanted to control them.

Once Amlici was made their king, he ordered them to take up weapons against their own people. He wanted to force everyone under his rule.