Aliens look upon the scene and realize that the only thing needed for conquest is to make the humans turn on each other.
The theme of The Monsters are Due on Maple Street is that fear and suspicion can be destructive. First, Charlie shoots Pete out of suspicion. this is outrageous considering that they had both been friends for a good amount of time. Second, when no one else's tools work, and Les' car suddenly turns on, the whole town creates a mob. This is terrible because Les didn't even know what was going on, but everyone was so afraid and suspicious that they immediately turned on him. Finally, as aliens look upon the horrendous scene, they realize that emotions can be as powerful as a gun or a bomb. Fear and suspicion can be destructive forces.