One Idea I think would make the game more interesting would be military division and naming.
To start, your military would be grouped into a series of units, for example 6,000 soldiers would form an infantry regiment, 3 regiments would form an infantry division, and divisions could be lumped together would form an army. 500 tanks would be an armor regiment, 3 regiments would be an armor division, and so on. There could also be hybrids like a mechanized division which would be 2 infantry and an armor regiment. Note that these numbers and names are completely arbitrary. When army units are recruited, they would be automatically put in an unfilled unit and when a unit is full, a new one is formed. When all the soldier in a unit are killed or dismissed, the unit simply goes away until more troops are purchased. There could be a units list page where you could organize all this, and when attacking you should see a list of your units, and be able to select all or some you wanted to send out. To make things simple for people who don't want to bother, the default option could be like it is now, one huge army, until someone decides to divide up their army.
It would also be neat to allow players to name their units, you could have "1st light infantry regiment", "23rd armored division", "2nd army", or whatever you wanted, I think it would add a very neat personalization/rp element to your army, make war more interesting and get you even slightly invested in your soldiers.