I think it was the influence of a more cosmopolitan outlook, it was certainly a first, afaik, but that is also an over gloss, it was more complicated of course, but that is the traditional textbook take. I personally think that it depends on the time and place, while mercy has been developed by today, it's always been present in individuals, there are surprisingly modern examples of this type of behavior, I would think that the knowledge of past behavior like being discussed was also not necessarily the norm, but those bizarre headline grabbing scenarios of today.