I'm confused by your comment. Are you proposing Switzerland as a "peaceful" country as a counter example? Due to mountainous terrain, they are fairly "isolated"/protected from invasion (one of the points above re what works to provide long term peace) and they also have about 2/3's of the adult (male?) population as part of a standing militia (which is in line somewhat with another point: "military supremacy").
Unknown (at least by me): "A man of peace must be strong".
I don't necessarily agree with all the conclusions drawn by the OP but I don't see how Switzerland is some kind of "counter example". Please clarify as I am honestly baffled.
Go check out sub-Saharan Africa, and see if that aphorism holds.
If you can think of more than just guns, Switzerland is a counter-example because of its politics - instead of the OP's suggested "Japan should just join in the next war, it's necessary to save it's society", Switzerland has pursued a long policy of neutral politics. It doesn't "simply join in on wars on whatever side looks stronger". It specifically avoids doing so.
What I'm pointing out is that it's not the guns that make the society polite. Sub-saharan africa is a vast conglomeration of countries and tribal societies, bigger than the US and Europe combined, and there you are calling it an 'exception'.
And nice job dodging someone trying to help you be less 'baffled'.
> Oh, and just to have a counter example: Switzerland
The Swiss are a strange bunch of people. As recent (or as long ago) as 500 years Machiavelli was praising their military spirit compared to the mercantile and money-oriented one of his Florentine fellows. He was predicting that the city of Florence's reliance on mercenaries instead of building a military spirit from the bottom up would finally lead to its submission. He was of course proven right, because while the Swiss have managed to preserve their independence through the centuries Tuscany was soon to fall under external dominance, but it begs the question if we would have been better off with a more militarized Florence but presumably less inclined to works of art (so no Michelangelo or Galleria degli Uffizi), or if it's ok that things happened just the way they did. Also, see Sparta vs. Athens.
Oh, and just to have a counter example: Switzerland