Einstein said "Nothing will benefit human health and increase chances of survival for life on earth as much as the evolution to a vegetarian diet."
Ayurveda recognises three gunas, or qualities: sattvic, tamasic and rajasic. Sattva is a gentle spiritual, peaceful quality, tamas is lazy and rajas is violent or aggressive. When an animal is killed it is full of rajas. When we eat the meat we take the rajas of the animal. Eating meat gives us a rush, a surge of adrenalin, passion... all of which is quite addictive. This rush can also be mistaken for strength, or even as the antidote anemia.
Though he wasn't actually vegetarian himself for long, Einstein long supported the idea, saying "It is my view that the vegetarian manner of living by its purely physical effect on the human temperament would most beneficially influence the lot of mankind." So maybe, on a simplistic level, our appetite for war and violence would naturally subside if we stop taking such rajasic food and lifestyle. Internal, daily violence adds up on a world scale.
But this theory doesn't explain Hitler....