To put it simply:
Units can only stack and not form cohesive fighting force.
Only generals can form armies.
Generals are the sovereign, descendants and champions.
The Charisma attribute from generals (quite underwhelming at the moment) would also influence how many units there could be in an army.
Here's other points, from my previous ill-fated thread, that I would love see included:
Auto-send bug reports
There's many examples of games and applications that spare the user from having to learn how to post a bug report. Please add an automated option for this. There's sure to be a substantial amount of valuable technical data that is being lost due to the lack of such mechanism.
Make visual distinction between quest huts that can be accessed and those that are above current adventure level. Indicate in hut's infocard which research needs to be unlocked to access it. Make option to "come back later" if player does not feel ready to enter quest hut, instead of having it disappear altogether.
Let descendants help sov spread magic. It's not fun to have sov's essence decline considerably while those spoiled brats have theirs intact. Alternatively, create a limit on the amount of essence a channeler can give. That limit could be increased with research.
Thank you for reading. Feedback is appreciated!