Napoleon executed the traitors to scare the other animals and keep them from speaking their thoughts/ as an example to the other animals to show them what will happen in they go against him. He does not want anyone to remember what truly happened because they will realize how their lives are worse now than when Jones was in charge. He does not want the animals to rebel against him. This helps Napoleon for his leadership because all of the animals are shaken and miserable because of the executions. Now, they are not going to want to speak up at all.