I've re-organised the unlocks for unit parts such that there are now two weapons in each era, one ranged and one melee, which should let players unlock new units at a fairly steady rate.
I've also added fourteen new units, mostly as side-grades for light and heavy cavalry when the player doesn't have horses or oil.
Mounted Warror: early ancient era light cavalry, before spears are invented
War Dogs: Classical era light cavalry, alternative to Horseman that doesn't require horses.
Armoured War Dogs: Medieval era version of the above
Dragoon: Renaissance Era light cavalry, between horseman and cavalry
Bicycle Infantry: Industrial Era light cavalry, alternative to cavalry when lacking horses.
Chariot: Ancient Era version of Heavy Chariot (heavy chariot pushed forward to Classical Era)
War Wagon: Medieval Era heavy cavalry without horses.
Gunnery Wagon: Renaissance Era heavy cavalry without horses
Shielded Infantry: Industrial Era heavy cavalry without horses
Modern Infantry: Modern Era melee (mechanized infantry moved to Light Cavalry track)
Recon Plane: early Modern Era air fighter, cannot attack but can deploy to gain visibility.
Dirigible Bomber: early Modern Era bomber
Seaplane Tender: early aircraft carrier
Supercarrier: Information Era aircraft carrier
