While awful by today's standards, they recorded their feats because those awful actions allowed their civilization to thrive, even at the cost of others' perish

While awful by today's standards, they recorded their feats because those awful actions allowed their civilization to thrive, even at the cost of others' perishing. Plus, by boasting of your awful deeds, you're more likely to dissuade would-be challengers. It would be lovely if we had knowledge from the common man from throughtout history, but the common man wasn't typically the reason for domminance.