Alma 46:30

Now Moroni thought it was not expedient that the Lamanites should have any more strength; therefore he thought to cut off the people of Amalickiah, or to take them and bring them back, and put Amalickiah to death; yea, for he knew that they would stir up the Lamanites to anger against them, and cause them to come to battle against them; and this he knew that Amalickiah would do, that he might obtain his purposes;

Moroni thought it was not good for the Lamanites to get stronger. So he wanted to stop the people of Amalickiah. He wanted to bring them back and kill Amalickiah. He knew they would make the Lamanites angry and start a war. Moroni knew this was what Amalickiah wanted to do to get what he wanted.

Moroni didn’t want the Lamanites getting any stronger. So he decided to cut off Amalickiah’s group—to capture them and bring them back, and execute Amalickiah. He knew Amalickiah would stir up the Lamanites to attack, and that was exactly what Amalickiah wanted so he could achieve his goals.