I believe there's some sort of limit on my army size (the rule seems to be "six units per army", as best I can tell), but I find it hard to figure this out from the in-game UI.

  (1) It doesn't seem to be written anywhere in the interface.  I think this is important enough that it should be indicated somewhere (either with the army statistics, or maybe more subtly; e.g., by only providing as many "slots" in the UI as there is room in the army).

  (2) If I try to combine two armies that are too large, I just get a rude noise and the move fails.  There should be an indication of why it failed.  In fact, I think the UI should probably warn me before I click (change the cursor to the "illegal move" icon, and float text saying that the resulting army would be too large).

  (3) Sometimes, instead of getting the "error" noise, the game allows the move, but creates a second army for the new unit.  I was trying to combine my armies, and I didn't realize at first why the unit wouldn't join the army.

  (4) The army size rules seem to sometimes be applied inconsistently.  I've seen cases where the game refused to add one more Spearman to an army, even though I was sure it was under the unit limit -- but later allowed me to add a different Spearman to the same unit.  (sorry, no save games for this )

  I think part of the problem underlying (2) and (3) is that the same gesture is used to move to a location, or to move to a location and join an army stationed there, and the game seems to be guessing which one I intended.  In Galactic Civilizations, IIRC, you had to explicitly join armies (fleets); would that help here?