Said Plato...

Socrates tells Glaucon that meat production necessitates large amounts of pasture. Resultingly, it will require cutting off "a slice of of our neighbors' territory; and if they too are not content with necessaries, but give themselves up to getting unlimited wealth, they will want a slice of yours. Thus Socrates pronounces, "So the next thing will be, Glaucon, that we will be at war."

- Plato, The Republic of Plato