I've thought for a long time that when these things were said, it implied that the community in that day and age was not nearly as stupid as people today. Today the average Christain looking at that saying is a recipe for disaster.
The ancient hebrew culture is extremely expressive. So knowing that, if you look at the original law he was countering, "an eye for an eye", it was basically the hard lesson on doing to others what you want done to you, this way you could avoid having your eye taken altogther. BUT if a person is consumed by the desire to get back at someone, it creates an endless cycle.
What he was saying is that a person should seek to make peace over seeking revenge. It was a fancy way of saying "you would seek revenge, but at what cost?"
It is fine standing up for yourself when need be. It is foolish to roll over and get kicked in the face willingly.
Also the western empire was causing issues in Japan, causing them to bite back, I'm assuming its not propagated in secular history books because they don't want people realizing that the western empire is much worse than even portrayed in the media and what they do allow in public history courses. This wasnt a case of Japan learning a lesson, but the cycle causing serious damage to one party. Because the western world has causes so much violence, particularly the US, a lot of money goes into military. Its similar to how a crook goes on so long and now no longer has rest and has to station himself in a hide out ot base with tons of weapons.