The tower actually has one, but the weakest setting can actually destroy a part of the continent they are in if i remember correctly from the novel.

he doesn't even have to go that far, I mean Amamiya is pretty much a self-sufficient little world, if he destroys the access portals that are known to people and just keep one somewhere where only they can access it and isolate themselves for a while, those people would fall into a decline because they were accommodated with the easy access to products that come from Amamiya and losing them suddenly would be chaotic for them