[yyyk]

Many ancient societies had a very different conception of 'good guys' than the modern one. It was very easy to justify very aggressive war with some of these alternative conceptions.

'Good guys are the ones who worship the right god(s) and therefore we get to kill the bad people next door', or 'Good guys are guys who serve the King/Emperor and anything that advances his glory is good', 'Good guys are cultured people and everyone else is a barbarian' etc.