I get what you mean about Europe rediscovering the importance of defense, but that’s about strengthening the military, not civilians owning weapons. The manga is talking about humanity being defenseless because no one had weapons, which is a exaggeration. In real life, countrys dont require widespread private gun/weapons (owned by civilians) just a good and equipped army
The manga is talking about already dystopian world getting even more dystopian (or even straight up dying), in which one horrible catastrophe - the great war - sown seeds for another by both banning arms and rendering most of the Earth inhabitable, so humans didn't even have anywhere to flee from the new threat.
I don't see why some people seem to be jumping to "author is against gun control" from that, when the backstory is clearly more about something similar WMD ban, but taken to extreme in result of world being already mostly destroyed, basically total pacifism becoming official ideology of what remained of humanity. Feels like Americans trying to insert their culture wars into foreign story yet again.
EDIT: If there was political aspect to it, it would be in context of Japanese pacifist post-war approach to army, including their constitution, where army should be a small and very strictly defensive force (similar situation as in Germany), and recent attempts to change it , mainly from the right, into more powerful and aggressive force similar to armies in most other countries. Which frankly I, in light of danger that China poses to the region actually support. It's not like modern Japan (or Germany) is about to invade anyone, unlike China which explicitly reserves to itself "right" to invade Taiwan if it ever will fully reject the "one China" philosophy.
