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?)

Solution 1:

If there is a general on a planet that is attacked, that general will command all units during the combat (applying his modifiers). The same applies for an invasion force, if a unit in that stack has a general, it will command all the units together.

With regards to the fortification attachments I do believe those have to be added manually, I will check tonight to confirm.