Very nice!
Excellent game; I have a few suggestions.
You should make it so one could make superficial changes, for example:
-You could change the Human's and Flag Guard's shield colour and shape
-You could change the flag colour and shape of each unit
You should also add in more units. Examples are
-Giant Eagles for air attacks
-Goblin or troll to defend against Eagles
-Catapult for massive artillary
-A cannon perhaps
Other changes you could make would be to make the game harder as it goes on. once I max out the health of everything, I can just walk into battle while barely taking any losses. You should also make it so one could control the other minions and their special abilities.
Last, but not least, please add a pause button.
Overall, I really enjoyed this game and I look forward to the sequel.