Hey man, you made an awesome game. Did you take inspiration from games like civ5/6? It's fun :D Just a few ideas: (I know it takes a long time, but if you ever need ideas here's some o3o)
. Horses around the map that can be tamed with the right technology
. Horseman and cavalry
. Catapults and battering rams that excel at combat against buildings
. Maybe boats?
. Training grounds to increase the strength/speed of military units
. Walls and defensive buildings
. Maybe a 'patrol' option for units so that they can patrol areas for enemies?
Great game man. Really enjoying playing it :D