Can I combine or merge land-armies, or use one general for multiple armies?

So I've just recruited a stack of armies to defend my homeworld (there's an uppity bunch of religious freaks next door, and we're Fanatic Materialist); but after recruiting them and hiring a general, the general is only applying to the first army I recruited.

Do I need a separate general for each army!? (And similarly, do fortification ‘attachments’ have to be built repeatedly for each army?)