Great game, but i have some suggestions:
Game modes: nothing crazy, just 2 game modes, Turns (which allows you to play for a set amount of maximum turns) and Infinity (play for as many turns as you want without a limit)
Espionage: Add 1 new unit which will mainly provide intel about the enemy's location, they have 0 support and only 1 defense, making them extreamly weak but capable of making themselves invisible for 1-2 turns at a time.
More Maps: more maps such as Pangea, continents and more.
its not neccecary to add everything, but these would be a great additions to the game