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>Either way you will almost certainly have a conquered population that is hostile to the conquerers. Do you think it matters who started the war?

In my layman's opinion, at the end of the war either the aggressor has won or the defender. If the aggressor has won it is well possible that the aggression and aggressive attitude towards the conquered "enemy" will continue. If the defender wins then it is possible that the defeated aggressor will accept the error of their ways and be amenable to working together to overcome the past and atone for the mistakes made. In other words the winner will, imo, set the tone for the attitude each side takes towards the other.