Hobbes assumed that if not for the state, humans by nature would live life that was solitary, poor, nasty, brutish and short. Implied here is that aggressiveness is innate in human beings. Plato thought otherwise as is explained by Angie Hobbs (sic) in the last Philosophy Bites.
Where Hobbes assumes a nature state with war of everyone against everyone, Plato lets Socrates describe a bucolic state, where a simple rural society leads a peaceful but abstemious life. War enters the scene when man develops desires for luxuries, specifically Sicilian sweet meat and Corinthian call-girls are mentioned. It is accepted by Plato these desires are innate and that the scarcity of Sicilian sweet meat and Corinthian call-girls will inevitably lead to war.
He questions however, if man's desires necessarily need be directed towards the scarce pleasures. He argues, by that time the desires have been corrupted and that is where aggression kicks in, but innately there is just desire. If desire could be directed to elated things, that are not scarce, aggression need not come out. That would show, aggression as such is not innate.
More Philosophy Bites:
Thought experiments (and Avicenna).