It's more a matter of logic and human nature. The Japanese have been essentially traumatized from being nuked and then being officially occupied by the US for years (unofficially still occupied, given all those military bases). A good amount are against doing anything that'll "rock the boat". General MacAuthor (the guy who led the invasion and occupation of Japan as well as made their Constitution) designed the Constitution so it's extremely difficult to update (need a super majority of the Diet, before a national referendum). A continuous, overt US presence means they can easily apply a little pressure to prevent any Constitutional changes, while any actions without such change would be illegal (and the Japanese are generally sticklers for the law). If there was anything that the US really wanted to change (can't think of anything, since it serves them well as is) they can always start a campaign, perhaps similar to La Tilde[0].
This[1] gives an idea of just how difficult it is to change the Constitution (there have been 0 amendments to date).
I really can't say much about Europe as I haven't done any research about any countries there.
It's a matter of you arguing over semantics. Useless ones too.
The US and in particular, the current president Trump has shown it is all useless. Every government has enough levers and workarounds to make it happen.
Trump has classified the attacks on Iran as "self-defense" so self-defense force, whatever... does it matter?
> and the Japanese are generally sticklers for the law
No, they're not. As usual you just take it at face value and read fake news. Japan's actual prosecution rate is ~30-40%. Post-indictment conviction rate is 99%. Guess why? They fudge the numbers, cheat the system and make it up.
Provide any evidence. This idea seems to come from your misinformed opinion and trying to provide some superficial difference between Europe and Japan