The main obstacle to universal election is not logistics as such. The most difficult problem is to keep a country where there are rivalling political parties united, avoid secessions and strong in the face of the enemies who can try to utilize the conflict for their purpose.
I refer you to this answer of minethis answer of mine. In short, the means of control (the weapons) available to the state were constantly improving compared to the weapons available to the rebels throughout the history. It is only when the state became strong enough to control any losing party within its borders, the elections over separate areas became possible.