Needs more diversity to keep things interesting
Games got a good idea going, except that its too easy after a certain point, based from what I've seen the game is all about strategy. However the game suffers the same fate as Final Fantasy tactics, you get an army of characters, but you only get to choose 4, which you make super super strong while the others are left in the dust. How could you fix this? well how about in certain battles you up or decrease the number of allowed soldiers? say in season 2 of the league battles, every 3rd battle requires the player to use 10 soldiers instead of 4 and in season 3 you gotta use 2 or 3. It would make for some interesting mix ups since I wouldn't be able to use my strategy of having my crusader tank everything with 2 archers while my cleric heals when I'm being rushed by 10 cavalry. Also, I didn't really see much point to using wizards since archers seem to be so much better at fighting at both melee and range. Perhaps wizards could cause random debuffs on whoever they hit? (damage over time, slowed attack/move speed, etc).
Another thing I'd like to suggest is when you get your warning on upcoming league battles. you should be able to see what kind troops your opponent has at their disposal so you can prepare accordingly for those opponents that give you quite a bit of trouble.
One last issue I'd like to cover is income. I've had to repeatedly restart my game due to the fact that I'd simply not have enough income to compete with my opponents, even when I've conquered all the possible territories I can grab with my current armies. Although the black market has a way of fixing this, it comes up far too late to give you any help aside from swapping gold for food so you can keep training. I'd suggest that since your troops can idle, how come we can't put them to work or something? It would also add some reason to have some troops in reserve, while your current squadron is fighting for you, the reserves are either training, resting or working to help make ends meet.
Aside from the flaws, the game had me going till the very end. I love the artwork and music you put into this. I hope to see more submissions by you.