Our first reaction to seeing harm is to attack those who do harm. This conflicts with the main way people learn. We learn by seeing how others act. If I am unknowingly or simply unsanely attacking someone else and am attacked in response, my thinking is only being reinforced. I feel hurt by the new attack and renew my attacks on a greater number of humans.
Attacking is ineffective in the long run. We create more enemies than we will ever destroy.
If we instead turn our attention to defending those people who ask for defense, we might make a difference. If I am am attacking others, find that I cannot do so, and am not acted against, I have time to think and to learn.
We can teach the world peace by defending those who ask for it--countries, cities and individuals alike.