Or "keep peace in your thoughts" if you believe there isn't a creator/protector/higher-level-organism.
Our brains work on quantum principles. This was how I realized telepathy was possible back in the late 90s when I read two articles, one said brains work not only on electrical, chemical, and biological principles, they also work on quantum principles; and the other said we've isolated one quantum principle in the lab, entanglement, or as Einstein called it, "spooky action at a distance."
There are many other quantum effects, my brain then told me, and I extrapolated that "The Protector" is powered by the quantum processes in our brains. Likely while we're sleeping. So if the planet didn't rotate to provide night, we may not have evolved a Protector (or at all).
Anyway, I just finished "Source Field Investigations" by David Wilcock; in it, he describes 7,000 Transcendental Meditation practitioners meditating and reducing world-wide violence for the duration of their meditation.
Thus, my answer is prayer/thoughts/meditation.
We certainly won't stop it with bigger weapons. Choose love, not fear.
I love you. I'm sorry. Please forgive me. Thank you.
http://fija.org - Fully Informed Jury Association
http://jsjinc.net - Jin Shin Jyutsu (energy healing)