Okay, two more questions…After you attack a territory with an air unit and you kill all of their units, must the air unit that you used, land back to any friendly territory within one space or does it go back to any territory within its movement range?
They can move to land in any friendly territory within the limit of their movement
If air units can not capture land territories, what’s the point of leaving men in territories like Yakut SSR? Wouldn’t the game just be about stationing all men at the borders?
You can try to do this, and many folks do. The risk is, once a break-through has been made in your front lines, you might not have any reserves to seal the breach. Also, no nation (except Russia) has an IC on the frontier, thus all builds have to work their way to the front from an IC.