Peace may or may not be a "modern invention", but it is certainly a much more complex issue than war. The world bleakly defines it as a period when war was not imminent or actually fought, but it is better if this is what is usually defined as a negative peace. It's often the best people can have, and they are grateful for that. But peace as it is generally understood today involves much more than that. Positive peace involves a social and political order of society that is generally accepted as just. Establishing such a system could take generations to achieve, and social dynamics could destroy it within a few decades.